Santander UK has raked in 1.1 million additional current account customers over the past year, which will bolster its plans to spin off from its parent company some time in the next 18 months.

The British arm of Spain's biggest bank said the surge in current account customers helped it post an 18% rise in pretax profits for the first half of this year, reaching £545m (€688m, $921m).

Santander's 123 current account, which has been aggressively marketed using celebrities such as Olympian Jessica Ennis, saw another 600,000 people sign up bringing its total customer base for this product to three million.

"Our aim is to become the best bank in the UK, for our people, our customers, our shareholders and the communities in which we operate, ensuring that everything we do is simple, personal and fair," said Ana Botín, CEO at Santander UK.

"Our performance, with results once again ahead of plan, reflects the strategic transformation we initiated in 2011. Since the introduction of guaranteed current account switching last year almost one-in-four of those customers who have moved banks have joined Santander UK. Satisfaction continues to improve for both our retail and corporate customers."

Santander UK is expected to be spun off from its parent group within the next 18 months and will be listed on the London Stock Exchange.