There was a deal posted by somebody last time halfords had a 10% offer on which stated you could get 20% by purchasing vouchers with the discount applied, then reserving an item and going in to the store and buying the item with the vouchers. This way you would apply the 10% discount twice.
I was too late to try the deal last time. But as this 10% offer lasts until Tuesday and the delivery date for vouchers ordered today is Wednesday, you should be able to complete it as I am trying to do.
I ordered some halfords vouchers online, and the 10% easter weekend discount was automatically applied to them. Their estimated delivery date is Wednesday or before.
I will reserve the item I want to purchase for store pickup on Monday or Tuesday (10% deal lasts until Tuesday). Which will reserve the item for 2 days. As long as the vouchers arrive while the item is reserved this should work.
The item I am buying is £100. It has the discount applied of 10% which makes it £90. I ordered £90 of voucers, which had the discount, making them £81. There was a delivery cost of £2 though. This meant I bought the £100 item for £83. The more expensive the item, the more worthwhile.
So you can get a 19% discount from halfords with 5 minutes of effort.