From the end of May, shares traded in the United States, Canada and Mexico will be settled - where legal ownership is swapped for cash - in just one business day (T+1), compared with two days at present on Wall Street and in Europe.

Charlie Geffen, who chairs Britain's Accelerated Settlement Taskforce, is due to send his report to the finance ministry by the end of next month.

"The question of how and when, and not if, is pretty universally held," Geffen told Reuters.

His report is set to recommend creating this year a technical group to thrash out common standards and processes for ensuring a smooth switchover to T+1 at the London Stock Exchange, banks, asset managers and other market participants.

Britain's financial services minister Bim Afolami said last month that Geffen's taskforce "will upgrade our back-office operations for the 21st century by moving from a T2 to a T1 settlement".

Geffen said creating a technical group and applying its standards would get the market "match fit" for T+1 during the first phase in 2025, before an actual switch in a second phase on a date that has yet to be decided.

Aiming for completion of the first phase next year gives time to cost and quantify the systems changes that will be needed.

"People need to know what they need to budget for in 2025," Geffen said.

Some industry officials say the actual switch to T+1 is unlikely before 2026.

The European Union has also said it is a matter of when, and not if, the bloc moves to T+1, and has called for coordination with Britain and Switzerland.

Geffen said it made no sense to set a date in stone for T+1 in Britain at this stage, not least because it needs to learn any lessons from the U.S. move.

"It does need to be mandated to make sure you get the necessary coordination," Geffen said.

(Reporting by Huw Jones; Editing by Mark Potter)

By Huw Jones