This article tells you how to simply disable this functionality within the current contactless cards without compromising the rest of the card payment chip and pin or magnetic strip capabilities.
The cards have a wire coil embedded within them that the card readers use to induce, without contact, a small electric current, which then powers the chip in the card. So, find the coil and break the wiring and the card can no longer be powered without contact and so will no longer function as a contactless card. A 2 minute search on Google lead me to this helpful post. The x-ray image (on which I have added measurements) of the card shows the wire coil within and it is also possible to make out the edge of the card.
Some quick work with a ruler and calculator enabled me to scale measurements from the image and find a suitable spot on the card (viewed from the front) that was easy to locate and that would not affect the chip, signature strip, card numbers, magnetic strip or hologram. Using a small felt tip pen mark the card, and then hand drill a 2-3mm hole. Your card should then look like this:
In fact I marked the back of the card as when viewed from the back, the hole sits neatly between the magnetic strip and the very end of the signature strip when in the right place, thus:
If you then look carefully, with some good sunlight, at the inside of the hole you should be able to just make out the ends of the severed coil copper wires glinting at you. Test the card in Starbucks or somewhere else with a contactless payment terminal and try to pay with it contactless. If you drilled the hole in the right place, and the Co-op have not moved the wires in your card, it won't work contactlessly.
I thought it was easier than changing banks. :-)