It's often falsely assumed that darker roasts will have more of a kick but lighter roasts actually have more caffeine content and (importantly) preserve far more of the subtle flavours of the beans.
So I suggest avoiding anything labelled as 'dark roast' or 'rich roast'. It tends to be only specialist coffee shops that offer 'light roast' coffee; with the supermarkets you'll need to settle for 'medium roast'. So this, on a special offer when you buy two packs, might suit you:
http://www.tesco.com/groceries/product/details/?id=258304545
The foregoing assumes that you want your 'kick' from the caffeine content (while being able to enjoy some wonderful flavours). If you'd rather have a coffee that simply 'punches you in the face' with its flavour, look for an 'Italian roast'. e.g:
http://www.tesco.com/groceries/product/details/?id=282362116
or
http://www.tesco.com/groceries/product/details/?id=253080263