UPDATE

I managed to get it working without rebuilding the site... I just couldn't blow the install away without having a small crack at it. Heres what I did:

Unticked all the Ubercart options (had to go through several rounds of unticking as I was working through dependancies that wouldn't let me untick certain boxes until others were disabled).

Uninstalled the Ubercart module from the uninstall tab of the modules page

Physically removed the ubercart module (I had previously also physically removed the ecommerce module) and untarred a new version just to be safe

Removed all the ImageCache presets back to just the ones I had before

Used PHPMYADMIN to drop all the ec_* tables remaining from the previous ecommerce module

Also dropped the one uc_ table that was left

cleared the cache and cache_* tables

used the content management part of the admin menu to find all old remaining products - at this point I realised I should have done this BEFORE removing ubercart. The old products now had no content-type and as such when I tried to edit them I got errors - I had to manually delete each one byt finding each node number, then going to (for example if it was node 8 ) /node/8/delete for each individual one

At this point I had a general scout around the admin section looking for anything ec or uc related - I don't recall finding anything else. I then reinstalled the uc module by initially just ticking the 4 core boxes and checked things - it all worked fine

So, hope that helps - its a bit 'hacky' but it saved me a reinstall.

Steve