The payment, which has been approved by the European Commission and HM Treasury, is intended to cover the costs Lloyds could have spent building a new IT platform when it carved TSB out of its own business.

Lloyds instead opted to provide TSB with a carbon copy of its own technology platform, thereby saving it money.

TSB chief executive Paul Pester has previously said his IT platform could support a bank three times its current size reflecting the scalability of what Lloyds has given it.

The payment was negotiated as part of the European state aid approvals earlier this year, when Lloyds needed to extend the date of its sale of TSB’s 631 branches from November 2013 until the end of 2015.

It was not detailed in communication to the wider market regarding the start of the float process, but has been disseminated in information to investors.

The prospectus is not expected to be published until the middle of this month.

The launch of the IPO process last Tuesday kick-starts a five-week process, which is expected to see TSB list by the end of the month.

Lloyds intends to sell approximately 25pc of the existing shares in TSB as the first step of its divestment process.

The offer is open to institutional investors and to intermediaries for their retail clients.

Retail investors who buy through an intermediary will be entitled to one free share for every 20 shares purchased, up to £2,000, if held for one year after the IPO.

TSB and Lloyds have been educating would-be institutional investors about the bank since the turn of the year in order to ensure sufficient appetite for the business.

As well as blue-chip UK investors, bankers working on the float have looked further afield, and it is known there has been some interest from the United States and the Middle and Far East.

The need for the divestment is a result of European state aid rules relating to the Government’s £20bn bail-out of Lloyds following its takeover of HBOS during the financial crisis.

Lloyds initiated a dual-track process to sell the 631 branches, with the Co-operative Group originally chosen as the preferred bidder.

But following the mutual’s financial problems, Lloyds returned to assess its options, and decided last summer that an IPO was likely to lead to a greater return.

TSB’s market capitalisation on listing looks set to be in the region of £1.5bn, roughly one times its book value.

The IPO process is being run by Citi and JP Morgan Cazenove for Lloyds, with four other banks including Investec and UBS assisting in the process.

Rothschild is acting as financial adviser to TSB.

A Lloyds spokesman declined to comment.