As people have mentioned already, the London Air Passenger Duty (APD) is the highest among all the European airports. It's actually higher for business class passengers too but it's charged only on outgoing.

If you have the time, fly in to London and take the Eurostar to Paris and fly out from Paris. You'll end up paying the same price total even after taking into account the Eurostar tickets but you get to visit 2 cities in one trip. But you'll have to play around with the dates, this obviously might not work a week before Christmas.

Are you flying economy or business/first? If the former I suggest that you save your miles and use cash instead. Compare the fees you'll pay vs. the actual cash price then decide.

The UK has the highest fees for award flights especially if you're flying business/first. Be prepared to pay thousands MYR in fees. This is not an Enrich problem however, I had to pay the same when flying/redeeming on United, Thai or Etihad too. My last flight in/out of London on business/first cost ~RM1,200 in fees.

Enrich redemption on Cathay requires a call to the Enrich call center. Do you homework before calling, good luck!