Just a word of warning on the Mercure - some of the bargain rooms are bargain for a reason. I tried it once with a good deal, and got a really uncomfortable bed and tiny room with noisy pipes clanging all night. I then (for some reason) gave it another chance when I saw another deal and got an even smaller room with an even more uncomfortable bed, and the shower didn't work. And the chambermaid barged into my room and woke me up at 7.20am on a Sunday morning. So definitely sticking to the Premier Inn from now on!
On that note, the Premier Inn Stratford proved that their 'good night guarantee' isn't just a advertising gimmick-we had a faulty air-conditioner that a) didn't seem to work b) made odd noises all night. We mentioned it on checking out, just as a 'by the way we didn't break it' thing and they immediately offered refund as we said it was noisy all night. Always had excellent service in general across all Premier Inns...Sir Lenny doesn't lie it seems