Heathrow to Penzance vs Paddington to Penzance

There are no trains from Heathrow to Penzance so you need to change somewhere, probably Paddington or Reading.

I've since discovered that I can catch the train to Penzance directly from Heathrow.

That’s not possible.

You can get the RailAir Coach to Reading and board the train there or go to Paddington on the Elizabeth Line or the Heathrow Express and board the train at it’s starting point.

Financially the most sensible way is to do exactly what you had planned. Buy an early bird Heathrow Express ticket to Paddington asap before travel (cheaper than the Elizabeth Line) then a Penzance to London on the day flexible ticket to guard yourself against the vagaries of international air travel.

Due to how the rail tracks are laid out it is impossible for a train to run direct from Heathrow to anywhere west thereof. Trains can only run east towards London.

Thank you.

It's very easy to take the Heathrow Express to Paddington, and then a train to Penzance. We recently landed at Heathrow at 9:50 am, took the HEX to Paddington (tickets purchased in advance) and then caught a 12:05 train to Truro, Cornwall. I purchased super off peak tickets with a 2 for 1 Railcard. We were in Cornwall by 4:30- which I thought was pretty amazing. You'll be going further to Penzance, but still it's all very easy.

We took the “midnight” train from Paddington to Penzance & it was so fun! Had a nice drink before bed & then tucked into our berth. Waking up just as we were rolling by the coast of Cornwall. Breakfast on the train & one has the option to use the showers at Penzance station if needed. Highly recommend!