Heriot Watt is ok, but if you have visited Teesside and liked what you saw then why risk it? Teesside gets great reviews for student experience and the MEng in Chemical Engineering asks for 280 to 300 points, not 240 (better check your information)! You will be spending four years at uni so go for what you know you will like.
Teesside promises to consider students who go firm for the next level down if they do not achieve the required tariff points for the course applied for, i.e. if you apply for MEng and achieve 260 points you might get offered the BEng Chemical Engineering, or for 200 points the Extended engineering (foundation year) programme. Its a good uni, good course and is student focussed - I would advise to go for the Teesside Offer.