One of the things that Mills points out is that apart from various river names (Lee or Lea, Brent), the only London name of Celtic origin is Penge, the SE20 suburb, which is derived from a Celtic/British/Old Welsh compound corresponding to modern Welsh pen ‘head’ plus coed ‘trees, wood’, exactly as in Pencoed in south Wales, literally ‘Woodhead’.
He comments further
Some make mock of Penge (an unusual name but not a pretentious place) by pronouncing it superciliously to rhyme with ‘blancmange’.
That is, they jocularly call it not pendʒ but pɒndʒ.
I have a friend who lives in Fulham ˈfʊləm. Sometimes in jest he similarly refers to it as flɑːm.
Another whimsical or jocular pronunciation distortion of this type is found in Liverpool, where the name of the district of Blundellsands ˌblʌndl̩ˈsændz (or in the local Scouse accent ˌblʊndl̩ˈsandz) is sometimes converted into the posher-sounding ˌblʌndl̩ˈsɑːndz, as if the final syllable belonged to the BATH lexical set (compare Alexander, commands and Ed’s recent comments about Castleford.)
Mills tell us that the etymology of Fulham is the rather boring ‘river-bend of a man called *Fulla’. In the Domesday Book (1086) it was spelt Fuleham, but in the Anglo-Saxon Chronicle (c. 900) Fullanhamme, with an OE genitive case ending -n on the personal name.
The street name Piccadilly has, Mills tells us, ‘rather a bizarre’ origin.
It seems that the name first appears as Pickadilly Hall in 1623, otherwise Pickadel Hall in 1636, as a (no doubt humorous) nickname for a house belonging to one Robert Baker, a successful tailor who had made his fortune from the sale of piccadills or pickadillies, a term used for various kinds of collars, highly fashionable at the time, for both men and women.
EFL teachers can use ˌpɪkəˈdɪli as a convenient demonstration of the ‘stress shift’ effect when we come to Piccadilly Circus ˌpɪkədɪli ˈsɜːkəs.