going on SSP and finding another job that is more suitable?

hi,

whilst i know (from previous experience) that it is perfectly legal to work a second job whilst recieving SSP from a first job,

(this case also backs this up:
http://www.qswblaw.com/wilsonbrowne-nt0002fb62.html )

ive had words with my employer and he "agreed" to pay me SSP as long as i took my first week as an "holiday" (i had just come back to work from holiday...) - whilst i understand he couldnt legally do this, i was going to recieve my holiday pay as a lump sum in a week or two due to contract and tax year things with work... so i "agreed"...

now, i am off work on SSP (due to sickness), and with my bad back, i am unfit for my first job... (drs note states this, and employer has made no effort to alter my workplace etc or even complete a risk assesment [i am taking high doses of codine - 30mg 4 times a day etc) which in itself can cause additional factors of risk (which my employer is aware of)

so, what i wonder is: am i legally entitled to start a new job, and continue claiming SSP off my first employer (the new job would be a checkout role in a supermarket, which is far less physically demanding than my current role) and also, would be hours outside of my current employment... (so i could technically work both jobs when i am "fit enough"...

whilst ethically i may get some "your wrong" etc's, legally, where do i stand (as i said, i know im entitled to continue working a second job, if i already had the post and i was still fit for that role...)

cheers...