I wouldn't touch it with a bargepole.
Consumer advice experts (e.g. Martin Lewis, BBC Watchdog, etc) frequently offer the opinion that extended warranties (which Mastercare's offer seems to be a beefed-up version of) simply aren't worth it.
Further, Mastercare has an appalling reputation!
http://www.ciao.co.uk/Reviews/Mastercare__59601
If you're an international jet-setter, who is constantly moving their laptop around the world, you might need cover for 'unintentional damage'. Otherwise, as long as you keep your coffee mug away from your laptop, you probably don't.
Laptop repairs can be rather pricier than those for desktops but the chances of you needing one or more repairs, totalling more than £189, within the next 4 years seems extremely low to me.
Save your money!