Pixel 8a 128GB for £231.99

When you say "You need to go past the basket page to see the £100 deducted", do you mean you have to actually purchase the phone before you see a discount being applied?
I have added it to the basket and gone as far as I can without actually purchasing and the price I see is £353/€431.

I've just received a partial refund from amazon for the import fee deposit paid towards my 8a purchase placed on 19th January.

Order Summary
Item(s) Subtotal:GBP 233.73
Postage & Packing:GBP 0.00
Total Before VAT:GBP 233.73
VAT:GBP 53.76
Total:GBP 287.49
Promotion Applied:-GBP 100.00
Import Fees DepositGBP 35.06
Grand Total:GBP 222.55
Payment Grand Total:EUR 268,29
Refund Total:€42,27

The reason for the refund was described in the email as follows:

Reason for refund: Export fee reduced

The following is the breakdown of your refund for this item:
Import Fee Deposit Refund: €42.27