Try vacuuming the keyboard or, possibly better, blasting it with a can of air duster. (
https://www.poundland.co.uk/air-duster ).
If that doesn't fix the problem you'll need to replace the keyboard. If you're mad enough to go to PC World they'll charge you an inflated price for a new keyboard (of perhaps £30) plus a flat fee of £60 to fit it. If you buy a new keyboard online it will only cost somewhere around £10 to £15. You can then fit it yourself (by following simple instructions on Youtube) or pay an independent computer repairer to do it for you. (Get a quote first. Some will want £50 but others will do it for £20).
If you urgently need to use your laptop though, buy a cheap wired keyboard from somewhere like Asda and plug it into a USB port on your laptop.