LONDON, March 28 - Britain's biggest pizza delivery firm Domino's Pizza UK & IRL Plc reported a rise in first quarter sales, helped by a recovery in Ireland, and said it was sticking with plans to open 72 new stores in 2012, including 12 in Germany.

Domino's, which operates the British and Irish franchises of the global delivery brand, said on Wednesday that like-for-like sales at the group's 660 established stores rose 3.5 percent in the thirteen weeks to March 25.

Like-for-like sales in Britain rose 3.6 percent, compared to 5.5 percent in the first quarter of 2011. Irish sales recorded a 1.7 percent increase, compared to a 10.5 percent fall in sales in the same period last year.

The company has benefited from cash-strapped Britons staying in to order pizzas rather than going out to eat during an economic downturn that has pushed the UK unemployment rate up to a 16-year high of 8.4 percent.

Although they are just part of the growth story, it is good to see our like-for-like sales continue to increase, said Domino's new chief executive Lance Batchelor, who took up the role late last year.

It is especially pleasing to see sales in the Republic of Ireland return to positive territory.

Trading had proved tough in Ireland after the former Celtic Tiger economy suffered the deepest recession in the industrialised world following the bursting of a housing bubble since 2007.

Domino's reported growth in its online business in the first quarter, with a 44.5 percent increase in total online sales to 59.3 million pounds ($94.7 million). Orders made using mobile platforms accounted for 16.4 percent of online orders.

We may have a softer comparative for the second quarter of the year but we will not be taking our foot off the accelerator, Batchelor said.

We have a number of marketing initiatives and other programmes aimed at ensuring our franchisees can profitably grow their businesses.

The chain added six stores in the first quarter and is confident it will achieve its target of 72 new stores in 2012, of which 12 will be in Germany.

The company opened six stores in Germany in 2011, and plans a further 26 outlets by the end of 2013, with a view to growing the business to as much as twice the size of its British operation.

Domino's said the first of the new German stores was being built and that it had found locations in the more affluent west of the country for other stores.

Shares in Domino's were down 2.2 percent at 461 pence by 0714 GMT. ($1 = 0.6263 British pounds)

(Reporting by Clare Kane; Editing by Paul Hoskins)