Great. Uncorked has a very good selection. I am seeking Quinta do Soalheiro Alvarinho Granit so know where to go!!I’d recommend Hedonism on Davies Street, perhaps not the cheapest but they’ve a pretty decent Portugal section and more generally for a visitor a great place to spend time idly browsing their fantasy bottles like 100 year run of D’Yquem or 5 gallon drums of Lafleur or whatever. If that doesn't work then Berry Brothers and Fortnum & Mason are a short walk away
Oh and if you are going from London to Norwich by train that means you’ll be going from Liverpool Street, so you should drop by Uncorked which have a modest selection of good Portuguese wine not worth making a detour for but you’ll be right there anyway.