While it is possible to interchange screens, you may want to contact a different repair shop.  Even allowing for higher prices in the UK, that quote seems excessive.   In the US, the screen costs about $200 -- and even with labor charge, it should be nowhere near that amount. [URL]  
I have an XPS 13 9360 with QHD+ touch screen that is constantly flickering. It's about 3 years old but has only started behaving like this recently. I have run all the Dell diagnostics and no issues are identified. Even updated all drivers to eliminate that possibility, but no change and still flickering. A local repair shop is quoting £600 to replace the screen but I don't think that's economically viable. If it is the screen that is faulty, I just wondered if it was possible to replace it with a FHD one, which should be much cheaper. I don't really use the touch screen in any case. I just need to be sure all the screen to motherboard connectors are the same. PC may even run faster with the lower spec screen.  
Dell XPS 13 8360 QHD+ Screen flicker