slag (pg. 52) -- Brit. slang for tart, whore, a loose woman.
Save the mark! (pg. 139) -- An exclamation of humorous astonishment, irony, contempt, etc. Often prefaced with "God".
maisonette (pg. 31) -- An apartment / flat on two levels with internal stairs, or which has its own entrance at street level. from Wikipedia.
treacle sponge (pg. 122) -- A treacle sponge pudding is a British dessert dish consisting of a steamed sponge cake with golden syrup or molasses cooked on top of it, sometimes also poured over it and often served with hot custard. from Wikipedia.
[Diana] having a high opinion of her deserts (pg. 88) -- I thought this was a typo of "desserts", but found this on Wikipedia: Desert, in philosophy, is the condition of being deserving of something, whether good or bad.
He seems to think laughter comes from god. (pg. 74) I like that phrase!
"Tough titties," said Ellie... (pg. 167) Language, Ellie!! secateurs (pg. 3) -- Brit. Eng. for pruning shears, or hand pruners.
winceyette (pg. 49) -- A kind of cotton flannel.
Baxi fire (pg. 26) -- An
underfloor draught fire, some sort of home heating device.
it's en suite (pg. 196) -- Brit. Eng. for including a bathroom.
donkey jacket (pg. 198) -- Brit. Eng. for a type of jacket worn by manual workers.
gamine grin (pg. 236) -- A girl or woman of impish appeal.
...skift of new snow... (pg. 204) -- An old southern term for a light dusting of snow.