I am going on holiday and from what I have seen, you will need to use hand luggage for the items you want the tax refund for unless it is bulky or a liquid.
If the items I want to claim for is neither of these but they will make the carry on heavier than the 7kg, would that be ok to do it at their office in the check in luggage?
The rep at border force call center was no help.
See: My goods are oversized or restricted