Airlines are set to bring the value of taking off and landing slots on to their balance sheets, with major companies able to book billions more in assets.

The move could see British Airways book an asset of up to £2.5bn significantly boosting its £11.3bn of assets and possibly allowing it to increase its debt.

Advisers from Deloitte say the airlines can now put the slots on the books because there is now a market for buying and selling the valuable taking off and landing times.

‘There has never been a situation where you have an “active market” until now,’ Graham Pickett, head of aviation for the firm, said. Under accounting rules, that meant the assets could not be booked. Pickett believes the airlines will book the assets ‘over the next six months’.

There has been increasing trade recently in the ‘pairs’ of slots ­ meaning a landing and taking off time ­ with some changing hands for up to £30m.

Heathrow slots are likely to be the most valuable.

BA controls 41% of those times at present and their value is estimated at between £1.8bn and £2.5bn, Pickett said. BMI holds 11% and Virgin Atlantic 3%.

BA’s next report and accounts is due in mid-May, and a spokesman said the company already recorded traded slots, but not the total value.