There are free VPN's, but they usually have a fixed data cap which is around 500MB-1GB.
ProtonVPN is really the only free VPN that I know of off the top of my head. It has no monthly data limits so you can use as much data to your hearts content.
Sadly though, it can only connect to 3 servers in 3 separate countries which are USA, Japan and the Netherlands. Also, the network speed the quite throttled down, so you might want to take that into consideration.
Even though the free version does not connect to the UK, you can still give it a try.
Full review is
here.