1930s: Council for the Preservation of Rural England (CPRE) is concerned at level of picnic waste from motor-coach 'day trips' excursions, and the then-new rambling groups, from the cities to natural beauty spots.
1930s: Women's Institutes (WI) take up the CPRE concerns, adding urban concerns about Bank Holiday Weekends, and coastal concerns about seaside beaches, etc. The WI lacks national backing or a coherent campaign.
1940s: Intensive recycling during wartime.
1950s: Soft drinks and beer are still sold in returnable/refillable glass and stoneware bottles, on which a cash deposit had to be paid. Lack of a bottle smashing 'yob' culture, outside of small parts of London and Glasgow.
1951-53: Conservatives launch first national anti-litter campaigns.
1954: Keep Britain Tidy Group formed by the Women's Institutes (WI), Queen Mother as Patron.
1958: Government gets behind Keep Britain Tidy. Conservatives propose and passed The Litter Act in Parliament.
1969: The famous "Tidyman" logo starts to appear on some packaging.
1970s: Keep Britain Tidy Group becomes more professional, uses celebrities in TV ads.
1970s: Rise of 'disposable' fast food packaging, non-returnable glass bottles, cans. Spread of fast food franchises.
1970s: IRA terrorist bombings cause the removal of litter bins in some urban public places.
1970s: TV children's series The Wombles (1973–1975, repeats later) introduces a generation of children to litterpicking as a hard but worthy activity.
1974: Keep Britain Tidy Group focussed only on those groups most likely to casually litter: school children, young men, smokers. Schools still able to organise pupils for litter picks.
1983: Conservatives proposed and passed the new Litter Act of 1983 in Parliament. Also the Environmental Pollution Act 1974.
1986: Mrs Thatcher forms a 'Litter Task Force' headed by Richard Branson. Leads to the Tidy Britain campaign, personally launched by Mrs Thatcher.
1980s: New large landfill sites needed across the country, to cope with the vast amounts of litter and packaging being generated annually.
1980s: Dog population starts rising rapidly, from a base of 5 million.
1980s: Spread of large out-of-town supermarkets, and more use of single-use plastic carrier bags.
1980s-2000s: Large increase in heroin addicts and drug dealers, who cause extensive localised crime and litter.
1990: Conservatives bring in the Environmental Protection Act 1990 in Parliament.
1990s: Health-and-safety doctrines prompt councils to move away from roving solo litter pickers, toward more vehicle-based street cleaning services. These then tended to become distinctly town-centre focussed, as the growing 'night-time economy' threw down ever more litter.
1990s: Schools and parents increasingly see litter picking as a 'demeaning' activity. This interacts with the new 'health and safety' doctrine, and some schools stop requiring litter picking by their pupils.
2000s: A growing rift between adults and kids, meaning adults could no longer admonish a kid throwing litter or smashing a bottle. The last soft drinks companies stop offering refundable deposits on glass bottles. Growth of the bottle-smashing yob culture.
2000s: Dog population is now much increased. 3.2 million more dogs are in the country than the late 1970s, meaning much more dog poo. Emergence of the bizzare and disgusting practice of hanging small bags of dog poo on bushes, trees and fences.
2000s: Rat numbers increased by 29% from 2001-2006, feasting on a new type of half-eaten fast-food litter. Consequent rise in the health risks of litter.
2000s: Terrorism fears after 9/11 cause the removal of litter bins in some urban public places, such as train stations.
2000s: Strongly rising population of urban foxes, which find ripping open bin bags at night easier than catching rabbits. This spurs the increasing introduction of wheely bins. This is followed by the rise of kerbside seperated-item recycling boxes for each household, which are often overflowing and/or opened up by high winds/foxes/cats, causing litter dispersal.
2000s: Rise in numbers of 'buy to let' landlords and university students — thus more fly-tipping of the left-behind goods of previous tenants.
* "Number and ownership profiles of cats and dogs in the UK".
* "KEEP BRITAIN TIDY CAMPAIGN AND RATS!", BBC News 30/09/02 and Google Books searches.