TSB is set to lose three senior executives within the next three months just as the beleaguered lender starts to pick up the pieces following its IT meltdown earlier this year.

HR director Rachel Lock will leave the bank by the end of November, while treasurer Ian Firth and chief marketing officer Nigel Gilbert are set to retire at the end of September.

Lock’s exit is understood to have been planned before a botched customer migration led to an IT meltdown this spring.

Firth and Gilbert were both expected to retire after the migration project concluded, a source close to the bank said.

But their departures come just as the bank tries to recover from the failed migration of customer data, which moved from former owner Lloyds Banking Group’s IT system to a new one managed by current owner Sabadell in April.

It left up to 1.9 million people using TSB’s digital and mobile banking locked out of their bank accounts.

Branch services were also affected.

TSB said it was making two promotions as a result of the departures, with its current marketing director set to takeover Gilbert’s role, while deputy treasurer Alison Straszewski would step in for Firth.

The bank said it was still in the process of securing a successor for its HR director.

TSB chief executive Paul Pester said: “Rachel, Nigel and Ian have been with TSB since the early days when we brought TSB back to high streets across the UK.

“I’m incredibly grateful for everything they have done to support TSB and I wish them all the best for the future.”

TSB’s failures have drawn strong criticism from politicians, including those on the Treasury Select Committee who have been scathing in their condemnation and called for Pester to be sacked.

TSB’s board and Sabadell have fully backed Pester to continue in the role.

It was reported earlier this month that TSB plans to double the size of its customer complaints team to 500 as the challenger bank ramps up efforts to address the near 135,403 complaints arising from the IT meltdown.

Around 37% of complaints have already been resolved.

TSB revealed last month that it had taken a £176.4m hit due to the migration failures, £115.8m of which was set aside for the likes of customer compensation and fraud costs.

Around £29.9m of that total accounted for lost income as it waived a raft of fees and charges following the service disruption, while £30.7m was linked to advisory costs and fixing operating defects in the system. It meant the challenger bank swung into the red over the first half, logging a bottom-line pre-tax loss of £107.4m for the six months to June 30, compared with a profit of £108.3m during the same period last year.