Economical with the truth - suggesting someone is telling unthruths without actually saying it thus avoiding being sued!
To be very annoyingly nitpicky: per my understanding, this splendid euphemism is not in fact a UK creation as such -- it originated / returned to health and vigour, elsewhere in the world (the general "economies made vis-a-vis truth" form of words, though not in that exact shape, has actually been around for a couple of centuries). According to Wiki, the exact "E.w.t.t." wording is identified as first showing up in two U.S. publications, independently of each other, in 1897; and it has been highly in vogue here and in other English-speaking areas, since its use in a trial in Australia in 1986.
An IMO lovely one along similar lines, of definite UK pedigree (coined by Winston Churchill in 1906), is
Terminological inexactitude.
https:en.wikipedia.org>wiki>Economical_with_the_truth
should, all being well, lead to the Wiki entry. (Hasn't worked as a link, I see -- I'm hopeless with links.)
"doing a runner" = leaving (a pub or whatever) without paying the bill.
My impression is, particularly used in and around London. I once heard, in London, an analogous expression "doing a dumper" -- dumping an item on someone without their consent, and promptly decamping. Not sure whether to regard this one as ingenious ongoing wordplay; or to think, "that sounds horrible".
"up the duff"; "in the pudding club"; "got a bun in the oven" and many more of even lower levels of acceptability = pregnant.
Genteel equivalent of the above:
In an interesting condition.