** UK housebuilders take a knock as Liberum issues arelatively bearish note just as valuations retest highs
** Thomson Reuters UK Homebuilding index upmore than 20 pct over last 12 mths, within grasp of record
** Barratt Developments & Bovis Homes, bothdowngraded by the broker to "hold" vs "buy", down 2.2 pct & 1.9pct, respectively. Barratt top loser on the FTSE
** Persimmon, down 1.9 pct & 3rd biggest UKblue-chip decliner, is broker's least preferred in the sector
** Liberum warns sector may have a "wall of worry to climb"with risk on inconclusive UK General Election, margin erosion &prospect of rate rises make rich valuations less palatable
** Recommends investors switch focus in the sector
** Broker's top picks are Berkeley, whose shareshave lagged & which Liberum upgrades to "buy" vs "hold", Bellway, which offers volume growth at low risk, & Taylor Wimpey - the best cash returner (RM: tricia.wright1.thomsonreuters.com@reuters.net)