After last month’s announcement that the largest retail store chain in the U.K. would start offering the iPhone, now comes word that Tesco is also slashing prices that would make even its U.S. cousin Wal-Mart jealous.

Tesco is selling the iPhone in their Tesco Phone Shops throughout the U.K., and they have announced that the base plan for service is a mere £20 ($32.54 US) per month, a full 1/3 lower than competing carriers, according to AppleInsider.

Customers will be able to purchase an iPhone 3G on a 12-month contract instead of the usual 24 months, at a slightly higher up-front cost of £222 ($361 US).

Tesco Mobile relies on the O2 network for its service, but signing up directly with O2, the cheapest iPhone plan is £34.26 ($55.74 US) per month with a two-year contract, and the device itself is free. Tesco Mobile is also offering an iPhone 3G for free with a two-year contract, but the monthly plan adds up to only £702 ($1,142.15 US) over 24 months instead of O2’s cost of £822 ($1,337.39 US). However, O2 customers get 600 minutes per month, while Tesco customers only get 300.

Chatterboxes who require unlimited calling with Tesco will have to fork over £60 ($97.62 US) each month on a 24-month contract, and if they want the newer iPhone 3GS, that will cost them £320 ($520.64).

The U.K. iPhone market has heated up in recent months after O2 lost its exclusivity in September. Competitors Vodafone and Orange quickly jumped into the fray to offer the device, and the Tesco Mobile deal is seen as a way for O2 to gain back some of their market share.