Not sure if people are aware of this, I don't think it was an option last year with Adrian Flux... they now offer 'flexdrive' which provides you with fully comprehensive cover to drive other cars (not the usual 3rd party cover). It was only £25 extra onto my annual premium so thought it was well worth it.
https://www.adrianflux.co.uk/drive-any-car-insurance/
https://www.adrianflux.co.uk/drive-any-car-insurance/