So my question is, is there a suitable template available? Are there applicable UK regulations providing guidance on this?
To be honest, this is the first time I've come across these FTC rules, or an objection from Google to an AdWords campaign on these grounds.
There are no specific English legal rules on this, and I'm not aware of any guidance from the regulatory authorities (e.g. the OFT).
The Consumer Protection from Unfair Trading Regulations 2008 do include some provisions that affect the use of testimonials.
A testimonial or testimonials page could amount to a "misleading action" in some circumstances.
The examples of unfair practices from Schedule 1 include:
4. Claiming that a trader (including his commercial practices) or a product has been approved, endorsed or authorised by a public or private body when the trader, the commercial practices or the product have not or making such a claim without complying with the terms of the approval, endorsement or authorisation.
I don't have suitable disclaimer text at present.