Update pt2 !
After a bit of research and thanks to a lot of help and advice from the pedelec forum users,decided to get a bottle battery installed,rather than getting my existing battery box re-celled, found a company called Kinisys based in Borehamwood -not too far from my house and once I contacted the owner,made arrangements to have the battery fitted,, while waiting for his mechanic to complete the fit, he offered me a few rides on a selection of bikes, got to be honest now,some of them are insane !!- it was almost possible to wheelie an electric bike -definitely not 250w and the advice to put my weight close to the front wheel on some of them was no exaggeration !.
Nice to have all that power available and I can see why for some the uk/euro limit is willfully low-anyhow,battery all fitted and time to test the Alien, took the bike home and put it on full charge-about 3hrs-result ! , bike is totally transformed and holds 18.2 on the flat like its no tomorrow,speed drops slightly to 11.2 on hill climbing but with assistance from me soon picks up again. all in all ,a worthwhile upgrade- battery is rated at 36V 11.4AH and the duration so far was yesterday managing 24 miles with a mixture of throttle and pedelling before the red light went out-even on orange,the battery was doing its thing,not as lively but still there, and this is in cold conditions going to work at 6.30am !,, battery should improve when the weather warms up I think. And the price was nice as well- £235 inc fitting,charger and 2 yr warranty !....