Don't you have any backup tea at the back of the cupboard? The slightly weird tasting one that someone got you at Christmas? The Earl Gray you got for that person who came round once? The loose leaf ones you normally can't be bothered using?
What's wrong with Earl Grey? Insufficiently English? Just curious since I do love me some bergamot, and want to make sure I have appropriate supplies for UK house guests later this year. Are you guys "1st flush Darjeeling or gtfo"?
UK house guests will most likely be expecting an English Breakfast Tea, if you insist on buying fancy ones with posh names. We don't call it that, we just call it tea. There's a couple of stray 'lemon' or 'green' in that list but most of them are bog standard blends of black teas called 'tea'.
Be aware that you will have to get lucky to make a proper cup of tea. Most of them supply slightly different blends to different areas of the country depending on how hard the water is.
I both love and respect the time you're putting in to try and make it perfect - but don't panic and overthink it.
If you include having a cup of tea at work, most of us are fine with "whatever hot water is available, from whatever limescale-ridden kettle is available, on top of whatever bog-standard teabags are in the shared kitchen, milk if it's not past the expiry date, without milk if it is".
You can get perfect temperature water, pre-warmed cups, filtered water etc, but most of the flavour in a cup of tea comes from a) leaving the tea bag in long enough to make sure it's strong enough, b) how hard the tea-drinker's workday or journey was.
Be aware that you will have to get lucky to make a proper cup of tea. Most of them supply slightly different blends to different areas of the country depending on how hard the water is.
I think that's really only Yorkshire Tea - I listened to an obituary of Warren Ford (the man behind the brand) and everyone remarked on his exceptional tasting and mixing abilities. Making hard water tea was his idea. I'm not sure the average punter could tell the difference unless they have their brewing set-up absolutely top-notch. Even then I don't think anyone would complain over something like that. But you never know.
Yorkshire's probably best (this applies to many non-tea related scenarios too), but nobody's going to turn their nose up at Tetley, PG Tips, Typhoo etc - any of the "normal" black tea ones would probably satisfy most Britons' request for "A cup of tea".
Earl Grey's more of a "1 in 20 people like it" sort of thing.