Heathrow: usually cheapest to the US and Asia

Heathrow is the most competitive long-haul market in the UK. On the transatlantic routes, British Airways, Virgin Atlantic, Delta, United and American all sell Business Class on the same city pairs, and that competition keeps fares down — particularly to New York, Boston, Washington and the West Coast. The same is true for the big Asian routes via Singapore Airlines, Cathay Pacific, Japan Airlines and ANA.

If you live near London or the positioning flight is cheap, Heathrow is usually the lowest-fare starting point for the US and Asia.

When a regional airport beats Heathrow

For the Gulf — Dubai and Doha — Manchester, Birmingham and Edinburgh have non-stop Emirates and Qatar Airways service that often matches or undercuts Heathrow, and lets you skip the connection to London entirely. For travellers in the north of England or Scotland, the all-in cost from a regional airport (no positioning flight, no extra night) frequently wins even when the headline fare is similar.

Manchester also has its own Virgin Atlantic and Singapore Airlines long-haul non-stops, so it is not only a Gulf-connection airport.

The Dublin angle

The biggest single saving is often not a UK airport at all. Starting the long-haul Business Class leg in Dublin avoids UK Air Passenger Duty — the £190+ per-passenger higher rate on long-haul premium cabins — because Ireland charges no departure tax. You position from the UK to Dublin on a cheap short flight, then fly Business Class onward. Dublin also has US preclearance, so you land in the States as a domestic arrival. The trade-off is the extra connection and the need to protect the self-transfer.

In short: there is no one cheapest airport — it depends on your destination and where you live. An advisor prices Heathrow, the regionals and the Dublin routing together and quotes the lowest all-in fare in GBP.