Online shopping is not eligible for tax refunds. To claim a VAT refund, you will have to purchase the good(s) from a Brompton retailer. 

You can find all the Brompton retailers here 

Please note that you will need to speak with the retailer to ensure that they are able to facilitate your request. This should be performed before making any purchase. 

To claim tax refund the item that you purchase should be for your own personal use and taken out of the EU within three months of purchase.

Further information for bikes brough in the UK can be found here .