The 1970s were a time of great change in British boys' clothes.
Boys were had seen  jeans and wanted to wear them even though their parents still weren't keen.
The Scouts had switched to long trousers in 1969, although the Cubs still insisted on shorts.
Caps virtually disappeared. State secondary schools continued to require uniforms, but even junior boys, with a few exceptions, now wore long trousers. A few Public schools still required shorts and most preparatory schools continued to require shorts. Many primary schools wore simple uniforms, usually simple grey jumpers, shorts, and knee socks.

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The style of short trousers which were still worn by boys for school and Cubs changed in the late 1960s and early 1970s. The long, baggy flannel shorts worn through the 1950s disappeared. Boys now wore much shorter  shorts, most commonly made of Terylene ( polyester ) blends.

In general, boys in Britain in the 1970s wore shorts up to the age of 12 or 13. At about the age of 11, many boys became self-conscious about being kept in shorts. This was brought on by the fact that at this time girls and women were also dressing in short shorts, called "hot pants" so by the late 1960s and early 1970s even conservative schools were shifting to long pants.

Play Clothes
The 1970s was the decade of bright colours, synthetic fabrics, and denim. Probably the most characteristic item of 1970s boys' clothing in England was short play shorts. Shorts for play were made from lightweight, synthetic fabric, and they were available in a wide range of bright colours, a far cry from the drab grey and black shorts of the 1950s and 60s. 1970s shorts reached only to the top of a boy's leg, unlike the much longer shorts of earlier years. They usually had an elasticated waistband, similar to sports shorts.

Even footballers of the time wore short, shorts.

Glen Hoddle in short, shorts!!!

Boys when not required by school or Cubs to wear shorts, generally liked to wear jeans which by the 1970s were becoming widely popular. Jeans had become a  fashion statement. Bell- bottom styles with studs and other designer work. Stone-washed jeans are introduced. Many British boys began giving their parents endless trouble to buy them jeans.

Boys began asking for all kinds of new fashions. Parents began to give increasing importance to what boys wanted. Income levels were rising. There were all kind of wild styles, such as purple loon trousers. Tank tops were also the "in" thing together with "woodies" which were fairly normal looking shoes except for the multi-ply wooden soles.

Shoes
The wearing of school sandals began to decline during the 1970s as children generally preferred to wear the tennis shoes  with jeans. School sandals were worn to school, but now mostly by little boys.

Hair
Propelled first by Elvis Presley and then the Beatles, boys moved away from short hair in the late 1950s and early 1960s. By the 1970s, many boys were wearing long hair of all lengths--including shoulder length long hair

More bizzare fashions probably appeared in the 1970s than any other decade.
Sport and suit jackets had wide, pointy lapels. Bellbottoms jeans were a popular fashion trend.

FASHION OF THE 1970's
The 1970's was the start of the disco era.
The youths of this time reflected the disco clothing and style. Hairstyles were long and free-flowing or afros during this time. They wore  tight pair polyester bell bottoms, a bright floral bodyshirt with a butterfly collar, and a nice pair of six inch platform shoes.
The colors used on the clothing were loud and clashing, and swirling psychedelic or flowers were the most popular prints. Along with disco fashion came synthetic fabric such as nylon, acrylic, and polyester.
Unisex clothing became really popular during the seventies; it was totally cool for a girl to be dressed like her boyfriend.

In the mid seventies you could see a change in the youth movements. Especially from England, which is usually on the forefront of youth cultures, where the punk movement started. The haircut could be recognized from miles away. It was painted in all sorts of colors and cut as strangely as possible. Clothes were mostly black and had rips which were kept closed by safety pins

Skinheads
The entire style of the skinheads is aggressive. A skinhead explained to the Times why: "You dress yourself to protect yourself. You've got boots on and they're your best friends. Your pants are tight so nobody can hold them. Your shirt hasn't got a collar so they can't pull it. The way things are going now you have to protect yourself."