take the mickey - taradiddle - tatting - tea cosy, tea cozy - telephone box - thick - third-year - ticked - timetable - tinned - titchy - toerag - toffee - top-of-the-range - tosh - trainer - treacle - treat - trifle - tripe - tuck in - tuffet - turf out - twiddle - twill
(Not strictly a British term, but in the interests of clarity it's being included here.) A kind of hand-made knotted lace, used particularly for edging or trimming (NSOED) - the kind of lace on Ron's first set of dress robes might have been tatting, for instance.
tea cosy, tea cozy
A cozy made to put over a tea pot for insulation, to help keep it hot.
"Awfully brave chap. Have you read his books? I'd've died of fear if I'd been cornered in a telephone box by a werewolf, but he stayed cool and - zap - just fantastic."
- Justin Finch-Fletchley on Lockhart (CS6)
The third-years had never had so much homework (PA15)
Schedule. At Hogwarts, each student is given his or her timetable at the beginning of the year, specifying the times of the various classes the student is taking.
A worthless, despicable person. This comes from an older sense referring specifically to vagrants, which in turn comes from, well, a person who uses a rag wrapped around the foot instead of a sock. (NSOED).
U.S. readers may have already encountered this one in Douglas Adams' The Long Dark Tea-Time of the Soul as the name of one of the characters (Odin's nasty little sidekick).
A kind of sweet; specifically, caramel.
All Harry's spellbooks, his wand, robes, cauldron and top-of-the-range Nimbus Two Thousand broomstick had been locked in a cupboard under the stairs by Uncle Vernon the instant Harry had come home (CS1)
It felt very strange to be standing here in Aunt Petunia's surgically clean kitchen, beside the top-of-the-range fridge and the wide-screen television...
- Harry explaining the dementor attack to Vernon (OP2)
Nonsense. "The slang tosh is a blend of the words 'trash' and 'bosh.' Bosh comes from the Turkish word for empty. Tosh means 'nonsense' or 'empty, worthless talk.'" (contributed by Sebastian Chen)
treacle (as in treacle pudding or treacle tart)
Treacle is a by-product of the sugar refining process and can vary in grade from very light Golden Syrup to Black Treacle (rather like molasses). Treacle Pudding is a plain steamed suet pudding which has warmed treacle poured over it. Treacle tart is a flat pastry case filled with treacle mixed with breadcrumbs and baked. In both dishes, Golden Syrup is usually used, as real treacle is quite strong in taste.
Blocks of ice-cream in every flavour you could think of, apple pies, treacle tarts... (PS7)
...the bubbling, treacle-thick Potion (CS12)
He felt it was a better use of his time to eat his way steadily through his steak and kidney pie, then a large plateful of his favourite treacle tart.
- Harry, tuning out Ron and Hermione's bickering (GF11)
Very good or very well. If something "looks a treat" it looks great, i.e., a treat to the eyes. "A treat" is a common phrase in some dialects, and can be used in other contexts, e.g., "I've polished this goblet and it's come up a treat".
A layered dessert of sponge cake soaked in sherry, topped with chopped fruit in jelly (jello), topped with custard, topped, in turn, with whipped cream. The top of that may be decorated with angelica, glace cherries, chocolate flakes or hundreds and thousands (tiny rainbow sugar candy pieces).
A tuft of stringy things (such as blades of grass, threads, or hairs) held together or growing together at a common base. Note that this isn't the same sense of the word as in the nursery rhyme "Little Miss Muffet / sat on a tuffet"; the word can also mean a little hill or mound.
Twiddle means to play around with, perhaps uncertainly, and is also a synonym for fiddle or fiddly; e.g. twiddly bits can be read as fiddly bits. Twiddly usually refers to something small - often a control of some sort that can be turned or rotated; e.g., a volume control can be twiddled, a light switch cannot (unless it is a rotary dimmer). Twiddled is usually used in a technical sense, e.g., "He didn't know why the radio wouldn't work, so he twiddled the knobs a bit." (contributed by Pat Gilliland)
"Listeners, that brings us to the end of another Potterwatch. We don't know when it will be possible for us to broadcast again, but you can be sure we shall be back. Keep twiddling those dials..." (DH22)
A woven fabric, sometimes used in making clothing, with a surface of diagonal parallel ridges, produced by passing the weft threads over one and under two or more threads of the warp (instead of over and under in regular succession, which is how a lot of fabric is woven). (The warp threads on a weaving loom are those that are strung by the moving part of the loom; the weft are the threads at right angles to the warp.) The word "twill" can also refer to the characteristic appearance of such fabric and the process of making it (NSOED).