First I need to tell you how disappointed I was that no one said anything about my (on purpose) glaring error in the second paragraph, before the questions began. None of you apparently realized that Guinevere was Arthur's queen and not a naked lady on a horse in Coventry. For shame.
Now I want to tell you that these answers come from supposedly authoritative sources, even official sources. So I am just going to give the answers as I wrote them down before I posted this. Some of your deviations from these answers are well taken, however. But let's begin with the "correct" answers.
1. A British Home Secretary (later a famous Prime Minister, of course) by the name of Robert Peel was instrumental in introducing several reforms in British criminal law, such as reducing the number of crimes punishable by death, but most memorably the Metropolitan Police Act of 1829, establishing the Metropolitan Police Force. The police were called "Peelers" because he was the one who pushed the Act through, and, later, "Bobbies" after his first name. Police are still called Peelers in Ireland.
I still need someone to explain the police structure in Great Britain. Is it a national force with offices in each town or are they separate entities like in the U.S.?
2. The last Queen of England was Elizabeth I. Case closed. Well, not closed if you want to fight about Wales. But that's the answer.
3. The longest reigning king was America's friend George III. 60 years. Almost.
4. The longest reigning queen was Victoria. 63 years. Her birthday is a national holiday in Canada. Officially "Victoria Day" it is more commonly known simply as the "24th-of-May" holiday.
For the record, Elizabeth II will pass queen Victoria when she is 89 years old.
Needless trivia: Queen Elizabeth's middle names are Alexandra Mary. Alexandra of Denmark was the consort of Edward VII; Mary of Teck was the queen consort of George V.
5. The first heir to the English throne to be given the honorary title of Prince of Wales was the son of Edward I. He (the prince) later became Edward II. Some would do well to note that in the question, the word "Prince" was capitalized. The Prince of Wales is different than a prince of Wales. So say I. But what do I know.
6. The Tay. (Not the Spey, as many think.) :)
7. Well, I can see this mythical place is still not agreed upon, but my answer book says Cornwall, and that Arthur was born at Castle Tintagel.
8. Going to go with the "official" Arthur Legend books here and say Castle Tintgel as the official right answer.
9. Quid is slang for pound. Sort of like "buck" is slang for a dollar.
10. Public toilets used to have a slot to put an (old) penny in. Hence "to spend a penny" is a British Euphemism used if a person gets up to go to the bathroom. As in "Gotta go drain my radiator" or "Gotta go see a man about a horse" or "Gotta tap a kidney." The British have even more cute things they say about taking a leak than even Americans. I found that out a long time ago. None of them make sense.
11. Spotted dick is a medical condition. The rest are just slang for various common foods. A gift for the British test-takers, a brick wall for Americans. Spotted dick is really a suet pudding with a dried fruit. But Sage's answer is the most usual. We'll go with that. Toad in the hole: sausage in batter, usually Yorkshire Pudding batter. Marmite? Salty tractor grease. Not yum. Parson's nose: the tail of a chicken or turkey. Butt is good. Arse is wrong. It's the tail. Chip butty? A butty is a sandwich. Chips are french fries. Go figure. But they say it is good. Bangers and Mash? Bangers are sausages. Don't ask me why. Mash is mashed potatoes. Truly delicious as is much pub food. I know I know... even better with onion gravy. At least in the northeast of England. Or so I thought until Sage said it was popular that way in her neck of the woods too. Okay, onion gravy ANYWHERE then. :) Another great pub food is the Cornish Pasty. And more. Let's stop here. I love the very thought of pub food too much.
12. The northernmost settlement in England, not counting islands, is Marshall Meadows in Northumberland.
13. Harold Macmillan.
14. A red dragon. Some say Griffin. Those some are wrong. Y Ddraig Goch for you Welsh purists.
15. The Bank of England.
16. Snakes.
Incidentally, the only venomous snake in the land of the spotted dick is the Adder.
17. Salisbury.
18. Scots about English.
19. Here I admit being mistaken by using the word "sea" as in Great Britain is an island. I should have used the word "coast". If you count the Channel as being "sea" as I intended, then the correct answer is about 70 miles. If you don't call it a sea, then the answer is not 70 miles. Sigh. What I meant to convey was you can't get very far from the water if you live on an island.
I think, and this is not from "official" sources, that the farthest you can get from the waters that surround the island of Great Britain is a point near Coton in the Elms (Derbyshire). At least that is what appears in one of my several reference books, but looking at a map I don't know if I believe it.
20. Cornwall. And how. Yum.
21. True. (Not counting the channel islands - which wouldn't matter if you did because the distance would be even more - the big stretch is from St. Agnes to Unst.)
22. A very old Welsh festival of literature, music and performance - dating back to at least the 12th century.
23. Greenwich Mean Time. (0 degrees longitude, or "the prime meridian" goes through the town of Greenwich. Probably the British are the ones who decided where 0 degrees was going to be on the map, too.)
24. Off into the Irish Sea to the east of NI. "Giants" after folklore stories. The Irish had a giant named McCool, much like our Paul Bunyan. I can't remember who the Scottish Giant was that he chased back to Scotland. Anyway, McCool was throwing huge rocks at the Scot and supposedly formed the spectacular causeway as they bounced off that fleeing giant. Some say one large rock that missed became the Isle of Man. I don't know. Maybe. But I do know the coast of Scotland there is also full of basalt columns (remember Fingal's cave?) so that lends credence to the land bridge theory. I say.
25. Windsor. Prince Harry, when in the army was called Cornet Windsor. Couldn't very well call him Harry in the army. His grandmother the queen, then princess Elizabeth, was known as Subaltern Windsor when she was in the Army (she was a heavy truck operator). The royal family, since at least George I, and maybe even further back, is largely of German ancestry, and the family wanted to sound more British during WWI, so they changed the name then (which was getting quite cumbersome by then anyway) to Windsor. Cornet and Subaltern are military ranks. George III, the American favorite, at least spoke English as his native language and was born there, unlike his two predecessors. Unfortunately, he stuttered so badly few could understand him anyway, so his English was largely wasted. He did have reproduction figured out though. What was the question? Oh. Windsor.