UK VAT Refund with Student Visa

Based on the experience of my friend and I in purchasing an item from Carphone Warehouse and getting the VAT refund at the Heathrow airport. For student with valid visa, obtain a letter from the university stating that you have finished with your studies. Items bought within the last three months of departure are eligible for VAT refund. Make sure the forms have been filled in completely for a more pleasant experience at the airport.

At the Carphone Warehouse
The Guildford store did not have form to issue the VAT refund receipt. They suggested that we try in London. So, we went to Oxford St. branch and they were able to issue the VAT refund receipt. No identification was needed there (At mothercare, the shop asked for my brother's passport. I guess at mothercare, they filled in the form for him where as at CPW we need to fill in the form ourselves). The administrative fee as charge by Carphone Warehouse is about 40% of the total VAT. So, effectively, the refund amount is only 12%. I'm not sure if the admin fee is a fixed amount or if it is a percentage of the total VAT. Anyway, below is the detail: 

Product Total Price:£149.00 (£124.17 before VAT)
Total VAT:£24.83
Admin fee: ~£9.93
VAT to refund:£14.90

At the Heathrow Airport
With a valid student visa, the officer asked for a proof/letter from the university stating that my friend have finished the studies. There were two options in submitting the VAT refund form. The first option is to hand in the form to the officer for processing later and there was no need to queue. We decided to use the second option in order to get a cash refund. There were two lines for the cash refund. The shorter queue is for less than three receipts and the longer queue is for more than three.
My friend has two receipts with £14.90 amd £2 refunds. The £2 refund cannot be accepted as it is too little. For the £14.90 receipt, only £11.23 was refunded after subtracting the handling fee of £3.67. Once again, I didn't know if the handling fee is a fixed amount or a percentage of the total amount.
Even though, there was a notice on the wall stating that VAT refund for electronic items need to be done after security, my friend managed to get the refund before security.

VAT to refund: £14.90
Handling fee: £3.67
Cash refunded: £11.23

In conclusion, my friend was initially charged £24.83 for VAT (20%) and £11.23 was refunded. This is 9.05% VAT on the product price before VAT. Effetively, less than 50% of VAT amount was refunded.