Originally Posted by
stut
That's a good point - to expand on that, if you can arrange your flight routing so it is:
Las Vegas - London then
Paris - London - Las Vegas
and take the Eurostar from London to Paris only, then you could save on the expensive UK APD (air passenger duty).
But be aware that straightforward return tickets are usually much cheaper and it's almost always significantly cheaper flying from London, notwithstanding the tax - it's simply a massively more competitive market.