how does the London leaving tax work?

What "London leaving tax"? There is no such thing - there is Air Passenger Duty which is a tax on airline tickets (and why on earth would it be priced in dollars rather than pounds?), but that is included in the cost of the ticket; there are no equivalent taxes if you leave by train, boat, car, or walk. If someone is trying to get you to pay something like this, demand a detailed breakdown of the fees - but it strongly sounds to me as though someone is trying to scam you and you should break off all communications with them immediately.

This sounds wrong. There is no leaving Tax from London. There may be other tax charges including the air tax and surcharges, but no Leaving/ departure tax for the UK.

If in doubt, inquire what these taxes are made up of, or try an book your flights yourself.

Good luck

Sounds like a really dodgy travel agent you have there - there is no 'leaving London tax' - - and who on earth are Emerance air ???? - I have never heard of that air line - I just wonder whether it is Emirates air - I have heard of them - you had better check who you are flying with as well.

as far as i know there isnt a leaving tax for london. what your travel agent might be saying is a fuel surcharge which airlines charge because of the high price of fuel. check with them again

Book your flight yourself. Why pay a travel agent to do what you can do for free!