Thanks to all for your help in this.
Have found a little bit more information on when the invalid prisoners were sent to Lewes.
It seems that they were housed on a prison hulk at Woolwich called the Unite(that e should have an accent, it was an old French vessel).Various inquiry and reports had found this hulk to be virmin infested and the conditions of the patients appalling, viz. the patients were filthy dirty and had no clean clothes for 5 weeks.They had no combs or towels for washing. There were no records of washing of blankets etc and bed linen was never changed. Thus its days were already numbered, when 'Defence'another hulk along side it caught fire. The Unite couldn't cope with the influx of semi-invalid prisoners from the Defence and they were all moved to the Invalid Prison at Lewes.
This is taken from W.Branch Johnson's The English Prison Hulks Phillimore 1970 and he quotes a report from the Times that the fire happened on 14th July 1857.So unless Lewes was already taking sick prisoners, it looks likely that it was only in existence for 3 years, 1857-1860 when it moved to Knapp Hill,Woking to a purpose built prison.
Another source is
http://freepages.genealogy.rootsweb.com/~blaker/reminiscences/commence.html This has a brief description by the Assistant Surgeon of the Invalid Convict Prison in Lewes, of the number of convicts and their types of ailment. Plus it confirms that it was indeed housed in the Old Jail,now the Naval Prison at Lewes.
Thanks once again
Clazy2000 Gill