Sarah Hughes Ruby mild, as it used to be called, is lovely stuff and gives a lie to the fact that mild is low gravity drink (it is around 6 percent I think). Remember having some once in the Goldon Galleon at Cuckmere which used to brew a decent drop of ale itself as well as stocking some...
Not sure what constitutes "micro" but Hopback Brewery, the inventors of the legendary Summer Lightning, would get my vote. Very partial to a drop of Titanic stout from the Titaninc Brewery of Stoke on Trent I believe. Not sure how micro they are either as this ale is available in Morrisons.