(Updates prices, adds details on weekly move, speech by BoE's Haldane)
By Jemima Kelly and Patrick Graham
LONDON, July 15 (Reuters) - Sterling slipped from a two-week high against the dollar on Friday as upbeat U.S. data boosted the greenback across the board, and the Bank of England's chief economist said Britain needed "muscular" stimulus to boost the economy.
In his first speech since Britain voted last month to leave the European Union, the BoE's Andrew Haldane said the central bank needed to come up with a "package of mutually-complementary monetary policy easing measures" in time for a rate-setting meeting on Aug. 4.
The pound fell almost 1 U.S. cent after the speech, and continued to weaken throughout the day, as data showed U.S. retail sales rose more than expected in June, reinforcing the view that U.S. economic growth picked up in the second quarter.
For the week, though, sterling was on track for its best performance in more than four months, with a more than 2 percent rise against the dollar, boosted by the BoE's surprise decision to keep interest rates unchanged rather than cut them, and by the anointing of a new prime minister.
By 1645 GMT, sterling was trading down 1.3 percent on the day at $1.3169, having earlier traded as highly as $1.3481.
"We think that extremely short positioning is going to play the dominant role in the next few weeks," said Valentin Marinov, Head of G10 FX research at Credit Agricole in London.
"Unless the data turns very, very weak in the coming weeks there is scope for further consolidation."
Many analysts, though, have recommended selling any rallies in the pound in anticipation of cuts in Bank of England interest rates and a slowdown in growth in the months ahead, with a number of major banks predicting it will fall to $1.25 or lower.
Sterling forward interest rates, which had been pricing in a strong chance of a cut in the bank's 0.5 percent base rate to zero by September, now only fully price in a single quarter-point cut.
Against the euro, sterling fell 0.8 percent on the day to 83.98 pence. For the week, though, the pound was up 1.7 percent against the single currency - its best week since May.
"I do think this rally is an opportunity to reload shorts," said a trader with one international bank in London. "Everyone's assumption is that there is a lot of bad news to come this year, so it does just seem like a matter of time before we go lower again." (Editing by Andrew Heavens)