I would suggest asking your current insurer for extra cover. I've done that before when having 2 cars, i.e. just bought new one and selling old one. Was a lot cheaper than £50 a day. But to back track a bit, are you aware of the law change?->
As part of Continuous Insurance Enforcement (CIE) it is a legal offence to keep a vehicle without insurance unless you have notified DVLA that your vehicle is being kept off the road by means of a Statutory Off Road Notice (SORN).
So you need to SORN it when you get it home
Plus, I always thought that "3rd party on other cars" only applies if the car is insured and owned by someone else. E.g. you can be covered to drive a mate's car