Vodaphone

I use GiffGaff.
You send away for a simcard in advance, and then activate the plan you want.
Works great all over the UK.
https://www.giffgaff.com/
Last trip it cost me about CAN $17. for plenty of minutes and data.

I have used Vodafone before, but GiffGaff worked better.

I don’t know anything about e-sims..
Never buy phone cards at airports….you have no recourse if they don’t work.

Last year I checked the vending machine at T3 baggage claim and the shop out in the terminal. Both had limited choices and were more expensive than what I could get at a Vodafone or EE shop in London.

Vodaphone is fine, if you are not tech savvy, or familiar with SIMs, wait until you can find a store, they will walk you through the options, install it, and make sure it works.

https://community.ricksteves.com/travel-forum/england/esim-activated-in-uk-vs-eu

This discussion should also be relevant.

My partner had Vodaphone and I often had better coverage in countryside areas with my Giffgaff Sim.
In Cities will be less of an issue

I have credited many a Giffgaff sim for when my US cousins vist,they are stunned at the relative low costs we pay.Activation is within 5 mins

I second giffgaff E-SIM! i am not tech savvy but signed up and activated the e-sim within a few minutes once i landed at Heathrow last month i “splurged” on the 20 gig plan (£15 GBP total) for my 28 days and had excellent service across England (London, Kent, York, Lake District, Liverpool, Bath, N Wales, and Brighton)

(I originally received the actual sim card in the mail but realized the e-sim was all i needed. Super easy and reliable.)

Thanks everyone for the helpful suggestions

Jim