Thanks to all who replied, ok I'll try and answer all the questions raised. What I know so far is :
The Issac in the 1841 census is the correct Issac, in Wharf Street, in fact it is Martha Fosters daughter he marries in 1844.
In 1851 he lives in Fleet Street St Margaret's with his wife Hannah and children Sarah, Catherine and Edward.
Mike correctly picked up his burial details in Welford road cemetary as being buried in plot CH734.
Issac's father is stated to be a frameworkknitter on his marriage certificate.
This is all I know, it is his earlier life that is a problem at the moment. The William Wormleighton that Newf mentioned only married Elizabeth in about 1830, so unless he was illegitimate that can't be his father.
Can anyone else add anything to this as I really have reached the 'brick wall' here?