Editor’s note: this is general educational information about how stabilisation and over-allotment work around a London listing, not investment advice. It is based on the legislation and rules listed at the end.

Analysis: a safe harbour, not a floor

The common description of stabilisation as price support gets the direction right and the strength wrong. Nothing in the regime obliges anyone to buy. The pre-offer disclosure has to say in terms that stabilisation may not necessarily occur and may cease at any time, and the post-period disclosure has to say whether it happened at all, which only makes sense in a world where the answer is often no. What the rules create is a permission with hard edges, not a guaranteed bid.

The edges are worth reading against each other. The 15% cap on the greenshoe and the 5% cap on any uncovered over-allotment set the maximum ammunition. The offering price ceiling determines when that ammunition can be used. The 30 calendar day limit sets when the permission lapses. A reader who knows those three parameters, all of which are published before trading starts, knows the outer bound of what stabilisation can do to a given listing, without knowing anything about the company.

What the disclosures do not establish is causation. The end of period report gives dates and price ranges, not volumes traded on each date, and it does not identify which prints in the order book were stabilisation. A share that traded quietly near its offer price for a month and then fell may have been held up by stabilisation, or may simply have had few sellers until the lock-up and index inclusion calendar changed. The dated disclosure of whether stabilisation occurred, and the prompt announcement of any greenshoe exercise, are the two documents that let a careful reader separate those stories after the fact.

One more feature is easy to miss. The FCA Handbook treats stabilisation carried out abroad under specified foreign regimes, including Regulation M made by the Securities and Exchange Commission in the United States, provisions of the Securities and Exchange Law of Japan, and the Securities and Futures (Price Stabilizing) Rules in Hong Kong, as conduct in conformity with the UK price stabilising rules for the relevant statutory purposes. Cross border offers do not need to stabilise twice under two rulebooks, and a London reader looking at a dual tranche deal may find the operative disclosures written to another jurisdiction’s template.

What the documents say

In the weeks after a company floats in London, a bank sometimes shows up on the bid whenever the shares slip toward the offer price. That buying is a regulated activity with a name, a fixed clock, a price ceiling and a disclosure schedule, and the person doing it has usually pre-arranged a short position in order to be able to do it at all.

The legal starting point is that supporting a share price by buying it looks a great deal like manipulation. Article 5 of the UK Market Abuse Regulation carves out an exemption: the prohibitions in Articles 14 and 15 do not apply to trading for the stabilisation of securities where the stabilisation is carried out for a limited period, relevant information is disclosed and notified to the FCA, adequate limits with regard to price are complied with, and the trading meets the conditions in the technical standards. Those standards are Commission Delegated Regulation (EU) 2016/1052, which supplies the numbers.

The clock

For an initial offer that has been publicly announced, the stabilisation period starts on the date trading in the securities commences on the venue concerned and ends no later than 30 calendar days afterwards. For a secondary offer it runs from the date the final price is adequately disclosed to the public and ends no later than 30 calendar days after allotment. Debt has its own rule: for bonds and other securitised debt, including instruments convertible or exchangeable into shares, the period runs from adequate public disclosure of the terms of the offer and ends either 30 calendar days after the issuer receives the proceeds or 60 calendar days after allotment, whichever comes first.

That window is the whole of the exemption. Outside it, the ordinary market abuse prohibitions apply to the same trades, which is why the aftermarket cushion around a new listing disappears on a date that was published before the shares ever traded.

The ceiling

The price condition is short and absolute. For an offer of shares or other securities equivalent to shares, stabilisation shall not in any circumstances be carried out above the offering price. For convertible or exchangeable securitised debt, the ceiling is the market price of those instruments at the time the final terms of the new offer were publicly disclosed. There is no exception for volatile conditions and no discretion to pay up.

This is what makes stabilisation asymmetric. If a new listing trades above its offer price, the stabilising manager cannot legally support anything, because there is nothing below the ceiling to buy. Stabilisation only has room to operate in a weak aftermarket, which is the aftermarket where its effects are most visible and most easily mistaken for a market view.

The short position and the greenshoe

The short position that makes stabilisation practical is itself regulated, under the heading of ancillary stabilisation. Securities may be over-allotted only during the subscription period and only at the offer price. The greenshoe option, which lets the stabilising manager buy the extra shares from the issuer or selling shareholders at the offer price, shall not amount to more than 15% of the original offer, and it may be exercised only where securities have actually been over-allotted. Any position resulting from an over-allotment facility that is not covered by the greenshoe option shall not exceed 5% of the original offer, which caps how naked the manager’s short may be. The exercise period for the greenshoe is the same as the stabilisation period, and the exercise must be disclosed to the public promptly, together with the date and the number and nature of the securities involved.

That structure gives the manager two ways to close a short. In a strong aftermarket, exercising the option at the offer price is the cheaper route. In a weak one, buying in the market both closes the short and supplies the bid. Neither route is open indefinitely, and neither exceeds the size of the option.

What has to be said, and when

The disclosure schedule is where the mechanism becomes checkable. Before the offer starts, the appointed central point must ensure adequate public disclosure that stabilisation may not necessarily occur and may cease at any time, that stabilisation transactions aim at supporting the market price during the period, the beginning and end of that period, the identity of the entity undertaking stabilisation, the existence of any over-allotment facility or greenshoe option together with the maximum number of securities it covers and the conditions for its use, and the venues where stabilisation may take place.

During the period, details of all stabilisation transactions must be publicly disclosed no later than the end of the seventh daily market session following execution. Within 1 week of the end of the period, the same central point must disclose whether stabilisation was undertaken at all, the date it started, the date it last occurred, the price range within which it was carried out for each date on which transactions took place, and the venues involved. Article 5(5) of UK MAR adds the supervisory leg: details of all stabilisation transactions must be notified to the FCA no later than the end of the seventh daily market session following execution, whether the entity acts on its own behalf or for the issuer or offeror.

The issuer, the offeror and any entity undertaking stabilisation must appoint one among them as that central point, responsible both for the public disclosures and for handling requests from the competent authorities.