RWE npower said on Friday it would slash gas tariffs by 5 percent from February 1, meaning four out of six of Britain's largest energy suppliers, which control 99 percent of the retail energy market, have cut bills.

The energy supplier, owned by German utility RWE, also said it would for two months waive cancellation fees for customers bound to fixed contracts who wish to change to a cheaper tariff following the price cut.

We are now at a point where costs, at least in the short term, can justify a price cut, said Paul Massara, chief commercial officer at RWE npower.

EDF Energy, SSE and Centrica all announced energy bill cuts this week, adjusting tariffs to a recent drop in wholesale prices as the mild winter weather and slowing economy have weighed on demand.

E.ON and Scottish Power have not yet announced price changes but analysts expect all large suppliers to make similar tariff cuts.

Britain's 'Big Six' energy suppliers increased tariffs between August and November last year, passing on steep rises in wholesale prices, which helped drive UK inflation rates to a three-year high in September and angered already cash-strapped Britons.

(Reporting by Karolin Schaps; Editing by Alison Birrane)