Buying Sim Card at Heathrow that has good data and good throughout europe

I found the SIM cards to be significantly more expensive at Heathrow than in downtown London.

wait until you get to a real supermarket or phone store, perhaps near your hotel?

I too suggest waiting until you get in town. Just head for the nearest Carphone Warehouse, they will explain your options and set up your phone. They sell from most all networks, so will steer you to the best option for what you want.

There are of course many other places (supermarkets, phone stores) that sell SIMs as well. Generally, if you purchase a SIM in one EU country (Switzerland not part of the EU) there are no longer higher roaming fees in other EU countries as there was 2-3 years ago. While Brexit may change this for the UK, I would not worry about it in the short term.

OKay so when I arrive I will need to go directly to the tube from Heathrow Underground to Eustin and take the train to Penrith, arriving in the afternoon. Can I buy one at the train station in Eustin or is there someplace along the way I can stop quickly to buy one . Or would I also be able to buy one someplace up Penrith. The next morning I leave on a trek and I need one before I take off🙂

I assume you mean Euston Station?

A very cursory online search indicates that there is a Carphone Warehouse on 145-149 Tottenham Court road. It seems to be very close to the Warren St tube stop and not far from Euston Station.

Thanks. It is only a 7 minute walk from the tube station. I might do that if I have time before train leaves for Penrith. I found there is also a Carphone Warehouse in Penrith not far from where I will stay. Curious about how much it costs to buy one with 2-5 gigs data and minimal phone usage for about 30 days.

your answer is on their webpage - https://www.carphonewarehouse.com/sim-only/pay-as-you-go-sim.html

Thank you so much for the info on carphone. This has all helped me greatly and I know what to do now. I imagine that the calling and texting are only within the country one is in and that these have roaming throughout Europe so can be used in France and Germany as well. So much cheaper than buying beforehand. Any recommendations on which company is best to go with.

which company is best to go with.

The one which has the best coverage in the areas you are going to. Ask the young person across the counter.

Don't expect any of them to have good coverage in The Lake District.

Stupid question... I found a Carphone Warehouse nearby Gatwick. From walking in the door to leaving how long should I expect to be in there to have someone help me get the right SIM, install it for me, make sure it works and pay for it? Never done a new SIM card before so completely new to this.

At a Vodafone shop the process takes me about 15 minutes plus time waiting to be served. I have a firm idea of my needs and relatively few questions. So if you have complicated needs or many questions, it may take longer. It can take another 30 minutes before the service becomes active.