He thinks he may have discovered the oldest item of plastic packaging ever to have washed up on a beach.

Oly Rush, 37, who last year swam around the Isle of Wight in a world record time to raise money for environmental charities, was carrying out one of his regular beach sweeps in Dorset when he happened upon the Doby bottle.

It is thought to date from the mid-1950s and the writing on it – including the ‘By Royal Appointment’ message – is still legible.

The moulded container, of which there is an example in the Museum of Design in Plastics, was discovered amongst the seaweed at Chapman’s Poole near Swanage.

Oly from Upton immediately knew he had found a vintage item of waste and exclaimed ‘she’s an old girl’.

Doby was produced by Thawpit Ltd of Manchester and the tops of its washing up bottles had to be pierced so the liquid could be squeezed out.

This bottle boasts that it is the ‘big new economy size’ of ‘1½ pints’.

Oly said: “This just goes to show how long plastics last.

“They are awful for the environment and while I’ve pulled tons of the stuff from local beaches, this is the oldest thing I’ve ever found.

“Whether it has been in the water all the time or has come out of a cliff I’m not sure, but either way it wasn’t doing any good.

“If we can all do a little bit to cut down on plastic waste then slowly the environment will improve and it’ll be better for us all and for wildlife.”

Oly’s 15-hour swim last year raised £12,000 for three environmental charities and to raise more awareness and money he is swimming around Grand Cayman in May.

He said: “It is 65 miles and will take me 30 hours, but I hope to raise as much as possible for Plastic Free Cayman.”

Details of Oly’s ‘Plastic Free Cayman’ swim can be found at www.ProjectPlanet.earth