Usage of *what* for *that* or *than* in BrE

Occasionally, when watching British television or movies, I've come across a construct that isn't used in AmE.

Using what as a replacement for that or than as a determiner or comparison.

Here is an example from the classic Monty Python Parrot Sketch:

C: Never mind that, my lad. I wish to complain about this parrot what I purchased not half an hour ago from this very boutique.

O: Oh yes, the, uh, the Norwegian Blue...What's,uh...What's wrong with it?

C: I'll tell you what's wrong with it, my lad. 'E's dead, that's what's wrong with it!

In AmE we would always say ... parrot that I purchased ...

I've also heard it used as a replacement for than in a comparison:

He thinks he's got bigger balls, what I got!

I'm guessing that in this case it's merely a colloquial deletion of than and should be than what I've got.

My question: Is this considered a colloquial usage in BrE? Or is it fairly standard in the Queen's English?

It seems to me that it might be colloquial based upon John Cleese's accent and intonation, but I don't have the ear for the British accent to pinpoint a regional vs. a socio-economic class of accent.

It is certainly not Queen's English, more an impersonation of a Cockney accent. Accent impressions are a constant feature of conversational English where people will imitate a voice to convey an impression of the type of person to whom they are referring

I agree with WS2 up to a point, The incorrect use of what in place of that is certainly not a feature of the "Queen's English" but knowing the parrot sketch like the back of my hand, I'd say that John Cleese was not speaking with a Cockney accent but with a stereotypical RP accent. A parody of those who disguise their low social class by faking a posh accent, i.e. Received Pronunciation. It is the shop keeper played by Michael Palin who speaks Cockney.

John Cleese's character is all the funnier because he is such an obvious dim wit; a customer who doesn't realize he's bought a dead parrot until it falls off its perch, who completely misunderstands the "foreign" word boutique, and yet uses clichè high register expressions and words — purchase instead of buy — correctly.

"I wish to complain about this parrot what I purchased not half an hour ago from this very boutique."

The use of what or wot in BrEng speech is a well-known marker of social status and level of education. And the dropping of g's and h's in one's speech is yet another common feature of Cockney.

Look, I took the liberty of examining that parrot when I got it home, [...] 'E's not pinin'! 'E's passed on! This parrot is no more! He has ceased to be! 'E's expired and gone to meet its maker!

It is this bizarre combination of standard and nonstandard English that might mislead one into thinking the use of what as a relative pronoun to be acceptable. This mixing of styles used to be typical among lower-class Britons wishing to be associated with a certain class. It is worth mentioning that the UK used to be obsessed with social class system until the mid/late 1970s and today that particular form of dialect or speaking style is becoming rarer (that at least is my impression).

Language and Social Class
Linguists have known for some time that differences in language are tied to social class. Ross (1954) suggested that certain lexical and phonological differences in English could be classified as U (upper class) or non-U (lower class), e.g., serviette (non-U) vs. table-napkin (U), one of the best known of all linguistic class indicators of England at the time. [...] The variable (h) refers to alternation between }h} and lack of }h} in words beginning with }h} such as heart, hand, etc. Unlike received pronunciation (RP), most urban accents in England do not have initial }h} or are variable in their usage of it. For these speakers who `drop their h's,' art and heart are pronounced the same.

That usage of what would be considered a colloquialism in standard British English. It is often used for effect by speakers of standard British English when imitating a speaker of a supposed (but not necessarily specified) regional dialect - just as in the John Cleese example. You will sometimes see it spelt "wot", just to make the point, for example in the phrase "wot I thunk" (ie "what I thought").