In my xr4i the engine had a ground off engine number, so when I re-registered it's new engine it said unknown, you don't, or didn't some years back need a receipt to prove the engine was yours, I even had my mate steve, a traffic cop look at it for me to see if it could be retrieved, but couldn't, I think you're safe unless a high value car, but who knows with dvla these days!!
tabetha