The terms of the foundation licence allow for use of Commercial radios and kits that conform to IR2028. IR2028 basically says that the kits must operate within amateur bands .
I cannot find any kit that conforms to IR2028.
Could an Intermediate Licence holder build a kit and have it tested by a full licence holder and then use it?
There is one exception however, in that if the Foundation holder is directly "operating under the supervision of a Full Licence holder". See Clause 7, para 2.76 and 2.77 of Ofcom's "Guidance for licensees" document.