Santander is bolstering its British foothold with the proposed acquisition of TSB, despite the recent underperformance of its own U.K. branch.

• Santander has agreed to buy British high street lender TSB for £2.65 billion from Catalonia's Sabadell in an all-cash deal.
• "We never thought of leaving the U.K. The U.K. is very important for us," Santander Chief Financial Officer Jose Garcia Cantera told CNBC's "Squawk Box" on Wednesday.
• The transaction further complicates the picture for consolidation in the Spanish banking sector, where TSB-owner Sabadell seeks to fend off the advances of BBVA.