Hi kevin,
There are superb good supermarket brands and there are are superb connoisseur brands. If your mom likes Yokshire Gold and Glenn Getty, then my guess is that she prefers strong tea over aromatic ones, and will probably do well with 'punchy' tea with a real good kick.
There are many supermarket brands, as Jim has recommended, you can pick your selection from there. Lipton has done well in continental Europe and the US, but not in the UK still...they are trying they are trying...
These are some snobby ones I'll recommend in addition to the ones other posters have recommended:
Harrods No. 14 - a blend of Indian, Ceylon & Kenyan tea. Good kick...
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Fortnum & Mason's Royal Blend - blend of Indian & Ceylon...good nuances, not that punchy though...
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Ringtons - they started out as tea peddlars! I like their Oriental blend when I need something not demanding, but their gift box is impressive...
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I like Bewley's irish Afternoon Tea, but I hesitate to put them in a basket meant for a gift. Still, it doesn't hurt to place one among the flashy big boys...
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Whittard - Breakfast Blend - Indian, Ceylon, Kenyan blend...though I find it not strong enough, I prefer the 1886 blend, which has keemun in it for nuance...
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Drury - haven't tried their teas yet...
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Fauchon - french company, I like their Le Siva blend (no. 43) which has darjeeling in it to give it some coyness, but the Morning blend (no. 36) is just for a nice balanced nudge...
kelmo http://www,fauchon.com