According to the British Library site, the use of nonstandard forms of past tense expressions like we was are common in some English dialects
The verb 'to be' has two simple past forms in Standard English - I/he/she/it was and you/we/they were. Apart from the special case of you, the distinction is, therefore, between singular was and plural were.
In some regional dialects, however, this pattern is not observed. In some parts of the country, speakers use was throughout, while speakers elsewhere use were exclusively. There are also dialects where the two different forms are used for the opposite function - singular were and plural was.
Usage examples are not hard to find in print:
1) What we was after was a couple of noble big di'monds as big as hazel-nuts, which everybody was running to see. We was dressed up fine, and ... - Tom Sawyer, Detective by Mark Twain
2) And we was in the lifeboat —I'd say about nine days. While we was in the lifeboat a German submarine surfaced. That's why I thought we might've got torpedoed too. - From Merchant Marine Survivors of World War II: Oral Histories of Cargo
3) We was on the come up. We all brought cars with the money we had stashed and the money we was making off the coke we was moving. - Lust, Money, Envy
but probably the more memorable usage was by George Harrison in the sound titled When we was fab.
1) where in the UK is this dialectal usage present?
2) what is the origin of this usage? An old usage survived from Middle English for instance?
3) is the above usage present also in dialectal forms of AmE?