British/local traditions

You speak of Hallowe'en, but the traditions in Scotland were very different from England - I'm sure someone will correct me on this, cause it's a long time since I've lived north of the border.
As children, we would dress up, knock on the doors of folks we knew. If invited in we would have to tell them who we were dressed as, and do a party piece (a dance, poem or a song). Sometimes we would dook for apples, other times we'd come away with sweets of a few pennies. More recently we lived in Aberdeen where Hallowe'en had taken on the American Trick or treat.
Also in Scotland (and parts of England) Hogmanay is still celebrated.

Have we had Easter Eggs yet? Apologies if so.
Trooping the colour?
Boxing Day and why it's called that.

Well dressing; Scarecrow Festivals; Edinburgh Tattoo; our local university has a team that enters in the Dragon Boat Races on the River; donkeys at the seaside; canal boat festivals; clog dancing; fell running; my brothers village still holds annual rush cart festival and brass band competitions, annual agricultural shows, May Queens,
Happy hunting & researching.

Up Helly Aa , May Day with maypole and Morris dancing . Pancake day with pancake races . Sports day egg and spoon , three legged race and sack race. Halloween Apple bobbing . Wassailing . Bog snorkelling . Winter lights festivals . Well dressing

In Bonsall, we have the annual Hen Race. It's slow going unless your a participant!

Beating the Bounds.

Re-enactments of various battles---joisting too.
Ancient camp-sites.

Whit walks
May Day - May Pole
Easter Egg hunts
Guy Fawkes night - treacle toffee essential followed by the dentist
Halloween
Christmas
New Year
Burns night
Valentines Day
Shrove Tuesday - Pancake day

I can't add to the wonderful list supplied by you gransnetters. I'm hoping to have a holiday in Scotland next year and would love to see some welly wanging. And what are Mischief Night and Up Helly in the Shetlands?

Jack in the Green, celebration of new growth in area’s of Sussex.

I think they are in a different category Carolpaint, just a matter of opinion.
Eccentric British traditions are often pagan in origin.

In fact, in Australia we had a public holiday on The Queen's Birthday but not in here in the UK.

For shame what about Remembrance Day, that also would include the members of the Commonwealth, Queens Birthday?

Here is a calendar:
projectbritain.com/curious/index.htm

Tetbury Woolsack races
The Cotswold Oylimpicks
Bourton in the water Football match in the river
Cheese Rolling at Cooper Hill
Afternoon Tea - utterly English!
Cream Teas - Jam first / Jam last
Yorkshire Puddings
Maypoles
Wassailing

Hope that helps

Guising at Hallowe'en (not trick and treat) and turnip lanterns (not pumpkins).

Shrove Tuesday. Lent? Can’t remember much about that. Aren’t you suppose to give something up that you really like?

Village fetes. Apple Days. Harvest services & suppers. Viewing "historic" castles, homes, & gardens via the National Trust, English Heritage, & Historic Houses Association. Anything connected with water! (We're an island nation.)

I'm interested in "proper" Halloween - what is it?

The Cooper's Hill Cheese-Rolling and Wake is an annual event held on the Spring Bank Holiday at Cooper's Hill, near Gloucester. It is traditionally done by and for the people who live in the local village of Brockworth, but now people from all over the world take part.

The Promenade concerts

Eistedfodd (already mentioned by Pantglas but worth mentioning again), children dress up to go to school in Welsh costumes and put on their own festivals.

Abbots Bromley Horn Dance. Six Antler Men, the Hobby Horse, the Fool, Maid Marion, the Archer and the two musicians have been dancing through Abbots Bromley and the surrounding area each year since 1226 and nearly 800 years later they're still going strong (but not this year unfortunately).

The Mari Llwyd

April Fool's Day and May Gosling (the same as April Fool but on May 1st and maybe just in Yorkshire).

Most counties have their own County Show each summer. Or they used to, until this year.

Horn dancing, sword dancing, well dressing, sweeps festival [Rochester], conkers, May poles

Welly wanging, Mischief Night, Up Helly in the Shetland Isles, scarecrow festivals.

Well dressing, mainly in Derbyshire.
Trooping the colour
Pancake races.