Problem solved.
Diesel bug. Changed filters, cleaned out tanks and pipes, heavy dose of bug killing additive. Engine running like a dream. Left Harleyford Marina, Cookham yesterday lunchtime arrived Grand Union this evening. Lovely trip. Went through Teddington 3 hours before high water and motored down to Richmond Barrage, picked up a buoy and had lunch. Watched barrage raise and then on to Brentford. Measured incoming tide at about 3 mph sot trip around to Thames Lock took about 30 mins.
Must compliment staff at Espa Marine for sorting issue out.
Martin