UPDATE 2-Tesco signs up technology platform for banking push

* Platform to be provided by U.S. group Fiserv

* Tesco Bank to focus initially on 15 mln Clubcard holders

* Tesco Bank has 6 million customer accounts

* Says will take time to set up current account

(Adds Fiserv deal, more from investor day)

By Mark Potter

LONDON, Nov 20 (Reuters) - Tesco (TSCO.L), Britain's biggest retailer, took a further step on its journey to become a force in banking by signing up U.S. group Fiserv (FISV.O) to provide the technology platform for its financial services business.

The supermarket group said on Friday, the second day of presentations to investors about its ambition to grow in retail services, that Fiserv would help it to make the leap from a collection of financial products to a full-service bank.

Tesco bought Royal Bank of Scotland (RBS.L) out of a financial joint venture in July 2008 and unveiled plans to double profits from its retail services businesses, such as banking, to 1 billion pounds ($1.7 billion) over several years.