Jo Crowley MADRID/LONDON (Reuters) -Santander's plan to buy TSB for 2.65 billion pounds ($3.61 billion) and boost its position in the UK came together just a few weeks ago, after the Spanish bank had been weighing a possible exit from Britain,

Banco Santander (SAN) on Tuesday announced an agreement to acquire 100% of the UK-based TSB Banking Group from Banco de Sabadell (BNDSF) (BNDSY) for an enterprise value of £2.65B in an all-cash transaction.

The Spanish lender is about to become the third-largest bank in the UK by share of personal current accounts, after the deal is closed.