It's possible that your order via Quidco will be accepted and initially track, but in the end the cashback payment is refused.
The whole point of Quidco and TopCashback is that it is a referral of a potential customer, (you in this case), who has not visited the target site, (BT in this case), so was unaware of what is available.
This is why they advise you to used a dedicated browser for ordering through them, rather than one you have used to visit the target site. You are passed through to a page on the target site that checks for their company's cookies held by your browser. Link
Given your recent order from BT, with all the relevant details, then it's quite possible the processing of the new order will spot what you are up to and decline the referral payment.
Or you could be lucky and they don't care as long as they get you as a new customer.
The indispensable man or woman passes from the scene, and what happens next is more or less the same thing as was happening before.
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