Yes it is. You need to get your refund from the last country you're in before leaving the EU. I assume you're having a stop over in Paris and not just transiting through. If you're transiting, you would need to get the refund in the UK as the customs check should be outside the transit area.
If you're travelling to another country within the EU before you
finally leave the EU, then you must show your goods and refund form to
customs officials in that country when you leave it.
VAT refunds for visitors to the UK
7.1.2 I'm leaving the UK for another EU country:
Show your goods, till receipts and refund form to customs in the last EU country you visit.
The deadline for exporting the goods stays the same regardless of how
many countries you visit.
Tax free shopping in the UK