January – Frederick Griffith reports the results of Griffith's experiment, indirectly proving the existence of DNA.
1 January – abolition of domestic slavery in the British Protectorate of Sierra Leone comes into effect.
6–7 January – River Thames floods in London; 14 drown. On 7 January the moat at the Tower of London (drained in 1843 and planted with grass) is completely refilled by the river.
29 January – The country's leading World War general, Douglas Haig, 1st Earl Haig, dies of a heart attack in London aged 66.
3 February – Funeral of Earl Haig.
8 February – John Logie Baird broadcasts a transatlantic television signal from London to Hartsdale, New York.
11–19 February – Great Britain and Northern Ireland compete at the Winter Olympics in St. Moritz, Switzerland and win one bronze medal.
12 February
An underground explosion at Haig Pit, Whitehaven, in the Cumberland Coalfield, kills thirteen miners undertaking clearance after an earlier fatal accident.
Heavy hailstorms kill eleven in England.
18 February – the Australian sport of Speedway is competitively demonstrated for the first time in the UK with a meet at High Beach in Epping Forest.
12 March – Malta becomes a British dominion.
1 April – Cinematograph Films Act 1927 comes into force, setting a minimum quota for British films to be shown in UK cinemas.
19 April – publication of the original Oxford English Dictionary is completed after 70 years with issue of the last section ("wise – wyze") in Oxford.
May – the Scottish county of Forfarshire resolves to revert to its historic name of Angus.
1 May – the London and North Eastern Railway's Flying Scotsman steam-hauled express train begins to run non-stop over the 393 miles (632 km) of the East Coast Main Line from London King's Cross to Edinburgh.
5 May – William Ralph "Dixie" Dean finishes the football season with a Football League record of 60 goals for First Division champions Everton.
7 May – passage of the Representation of the People Act lowers the voting age for women from 30 to 21 and removes remaining property qualifications, giving them equal suffrage with men from 2 July.
16 May – opening of Royal Tweed Bridge, Berwick-upon-Tweed, constructed from reinforced concrete to the design of L. G. Mouchel & Partners.
17 May–12 August: Great Britain and Northern Ireland compete at the Olympics in Amsterdam and win 3 gold, 10 silver and 7 bronze medals.
27 June – 25 people killed in the Darlington rail crash.
3 July – John Logie Baird demonstrates the world's first colour television transmission in Glasgow.
27 July – Tich Freeman becomes the only bowler ever to take 200 first-class wickets before the end of July.
26 August – in Paisley, May Donoghue finds the remains of a snail in her ginger beer, leading to the landmark negligence case Donoghue v. Stevenson.
15 September – Tich Freeman sets all-time record for number of wickets taken in an English cricket season.
28 September
Scottish-born microbiologist Alexander Fleming, at St Mary's Hospital, London, accidentally rediscovers the antibiotic which he will call Penicillin.
Dangerous Drugs Act 1925 comes into effect, placing restrictions on the use of cannabis.
10 October – Tyne Bridge opens, connecting Newcastle upon Tyne and Gateshead.
9–16 November – Radclyffe Hall's novel The Well of Loneliness (published on 27 July by Jonathan Cape in London) is tried and convicted on the grounds of obscenity due to its theme of lesbian love, following a campaign by James Douglas in the Sunday Express newspaper.
12 November – Randall Davidson becomes the first Archbishop of Canterbury to retire, having served for twenty-five years, the longest in this office since the Reformation. He is created 1st Baron Davidson of Lambeth three days later.
15 November – the Mary Stanford life-boat capsizes on service in Rye Harbour: all 17 crew lost.
22 November – following passage of the Currency and Banknotes Act on 2 July, the Bank of England resumes responsibility for issue of banknotes from HM Treasury and issues pound and (for the first time) ten shilling notes, the first to be printed in colour and on both sides.
23–25 November – a windstorm affects parts of northwestern Europe and kills 38 people, mainly in England.
4 December – Cosmo Lang enthroned as Archbishop of Canterbury, the first bachelor to be appointed in 150 years.
20 December – the first Harry Ramsden's fish and chip shop opens in Yorkshire.
24 December – first Festival of Nine Lessons and Carols to be broadcast from King's College Chapel, Cambridge, by BBC Radio.
Undated
Mond–Turner talks between industrialist Sir Alfred Mond and chairman of the Trades Union Congress Ben Turner on consensual approaches to industrial relations.
First high-voltage electricity pylon for the National Grid is erected, near Edinburgh.
Owen Willans Richardson wins the 1928 Nobel Prize in Physics "for his work on the thermionic phenomenon and especially for the discovery of the law named after him". This award is announced on 12 November 1929.
Heinz Baked Beans are manufactured in the UK for the first time.
British Home Stores opens its first department store at Brixton, London.
Uffa Fox launches his first planing sailing dinghy, Avenger, in the International 14 class and wins 52 out of 57 races. He sails Avenger across the Channel and competes in some races in Cherbourg Harbour.