Transport for London (TfL) has unveiled plans to sell part of its Tube fleet and lease it back, in a bid to raise funds to purchase new trains.

The capital's transport body said the move was "standard practice" in the industry, with a similar deal already in place for the London Overground and underlined the sale would not reduce the number of trains available on all Tube lines.

On Wednesday (3 January), TfL told the London Assembly Budget and Performance Committee on that the move was "a very normal sale and leaseback of rolling stock" to allow it to buy the next series of trains for the Piccadilly line.

"As is perfectly standard and common practice across the rail industry, we are looking at whether we could sell and lease back some of TfL's rolling stock, as we have previously done on London Overground," said a spokesman for the body.

"This would allow us to purchase new trains on London Underground's Piccadilly line, where there is a clear need for a modern fleet."

The contract for the new rolling stock on the line will be awarded in the first half of 2018 and TfL added it hopes to raise approximately £875m for new trains on the Piccadilly line by 2023.

London's transport authority has seen its budget come under pressure recently, due to a combination of factors, such as the fare freeze introduced by the Mayor Sadiq Khan, government cuts and a decline in revenue from advertising and fines.

"We have decided to press ahead with the procurement of the Piccadilly line rolling stock and will be looking to award that contract in the first half of 2018," Simon Kilonback, interim finance officer at TfL, told the committee.

"We have therefore made a decision about taking some of our existing rolling stock and doing a sale and leaseback of that to finance the Piccadilly line rolling stock."

However, the proposal was criticsed by the Liberal Democrats' Caroline Pidgeon, a senior member of the London Assembly.

Pidgeon, who is her party's only representative in the London Assembly, said plans to sell trains to lease them back in order to raise funds was "quite mad" but acknowledged TfL was facing financial constraints.

"You're going to be selling and leasing back rolling stock you've already got, that you wholly own, in order to give you the cash to buy new rolling stock? It sounds quite mad," she said.