Here’s a selection of Portuguese delis in London. We’ve not tried them all but those we haven’t
South East London
Rio Deli Small shop with Portuguese and Brazilian products in Bromley. Limited selection but can order seasonal pastries like

Luso Flavours Café and Deli in Welling has a wide selection of Portuguese produce, cheese, charcuterie, pastries
La Ciabatta in Catford is a café with a tiny shop at the back
South West London
Stockwell has many restaurants, cafés and Portuguese shops. Here’s a selection
Delicias in Wandsworth Road has been around for a while and is well stocked. You can order online for delivery as well. They also have branches in Victoria and Kensal Green, plus one in Suffolk. The Wandsworth branch has a café area and a wide selection of frozen fish.

Serrana in Clapham Road also comes well recommended
Taste of the Mediterranean has a good selection of frozen products (fish, rissoles, pastries, bread).
Madeira Deli in Albert Embankment, Vauxhall has a huge selection. They have other branches and do wholesale so whatever you fancy, they’re likely to have it

West London
Lisboa Delicatessen, in Golborne Road near Notting Hill Market and opposite Lisboa Patisserie is also well established

North London
Ferreira Delicatessen in Delancey Street in Camden Town has also been around for a good few years
Tamariz Deli in Acton supplies further North off London
East London
A Portuguese Love Affair Deli Café in Hackney Road won the best Pastel de Nata award in the inaugural 2018 Nata Festival so are a worth a visit even if just for that! You can also visit their shop in Columbia Road

Online
These all deliver in the UK:
Mercearia de Portugal also delivers across Europe