Experian have some useful information on their website. It's one of those sites where you can't link to specific pages, so here's what you need to do:
First, go here:
http://www.experian.co.uk/consumer/index.html
Click 'Questions'.
Click 'About your credit report'.
Click 'Other people'.
Read through that information and then download the (pdf) leaflet called 'Relationship breakdown' from the Click here for helpful credit advice during a divorce and separation' link.
Then download the form, or use the online procedure, for the 'financial disassociation' form. (Note that the website states that, in some cases of separation, Experian may require additional information. That form, however, should still be your starting point).
While you need to apply to all 3 credit reference agencies to check your own credit record, you should only need to contact one of them to get the 'disassociation' recorded. (This will then be passed on to the other agencies).
Once you've registered the disassociation, any credit application from your wife (using your address) would be treated with suspicion by a potential lender (and probably refused).
Chris