The Canada-led bank aims to raise about €100bn to offer low-cost defence loans and guarantees, which backers say could help allies rearm and let the UK finance projects more cheaply.
UK membership would require an initial capital commitment of roughly £1bn to £2bn over three years, a hurdle that previously fed Treasury concerns while public finances were strained.
Rachel Reeves had rejected joining, arguing the bank would do little to fix UK procurement and was geared more toward smaller firms in lower-rated countries; the UK instead committed £600m to the rival Multilateral Defence Mechanism.
Healey’s rethink could reshape how Britain pursues its 3% defence-spending goal, as he plans to set out a pathway in the 2027 spending review rather than fix a date in next month’s budget.