Confidential details of the 50-year lease that will turn Raven’s Ait into a sailing school have emerged, in the week a key council committee allowed the plans to go after a behind-closed-doors meeting.

Kingston Council is believed to have turned down a £1m offer to sell the island and allow 20 flats to be built, instead agreeing a £20,000-a-year lease, including one year rent free and guaranteed community use, with Stewart Marine.

The council’s executive committee agreed the deal last month, but Conservative councillors referred it to the scrutiny panel to examine the process used, why a lower offer was accepted and the proposed use of the island.

It also questioned whether the council examined relocating Albany Park Sailing Club.

An earlier deal for Antoinette Hotel to take over the island, agreed last November, fell through when the firm twice its original offer, and then backtracked on this figure and submitted an even lower amount.

Tuesday’s scrutiny panel meeting removed members of the public from the audience and spent over an hour discussing the lease in private after legal advice about protecting commercially sensitive information.

However, it is understood to contain clauses preventing the island being returned to the council in poor condition, guaranteeing continued access for Surbiton sea scouts, preventing residential boat moorings, and requiring consideration of council requests to use the island for additional services.

At Stewart Marine’s suggestion, the council will be able to nominate 10 days a year for free community use of the island.

The scrutiny panel recommended clauses relating to dilapidation and additional services be strengthened, and the council better define the community use.

Conservative leader Councillor Howard Jones said: “There were offers on the table from people who were willing to pay four times what Stewart Marine offered.

“That four times, in our view, could well have been a very good deal, but whether it was followed up sufficiently is something I cannot discuss fully.

“On the basis of what we were told, we were not in a position to make any other recommendation than the one we made.”

Ossie Stewart, the Olympic sailing medallist who owns Stewart Marine, said he was happy with the panel’s recommendations and hoped to open the sailing school next year, although the island could be used for community activities this summer if requested.

The council’s executive committee is expected to approve the recommendations next Wednesday, March 31, allowing the lease to be signed and renovations to start on the island.