Chancellor George Osborne will unveil a new 12-sided pound coin featuring the four symbols of the UK – a rose, leek, thistle and shamrock – emerging from a royal coronet, ahead of his budget on Wednesday.

The design on the tails side of the new coin is the work of West Midlands teenager David Pearce, who won a competition to create the image.

The new coin, which will be introduced in 2017, is the same shape as the old threepenny bit, which was withdrawn in 1971.

The chancellor announced plans at his budget a year ago to replace the current £1 coin because it has become increasingly vulnerable to counterfeiting. Around one in thirty £1 coins are forgeries.

While the shape of the new coin will evoke the pre-decimalisation period, it masks cutting-edge anti-forgery technology. The Royal Mint says the new pound will combine three features to make it the most secure coin in the world. It uses two colours of metal, has 12 sides and includes the Royal Mint’s anti-counterfeiting technology, adapted from banknotes and embedded in coins for the first time.

The design by Pearce, 15, a pupil at Queen Mary’s Grammar School in Walsall, was chosen from more than 6,000 entries in a public competition. The brief was to create a tails side which symbolises Britain. Entries included cups of tea, the weather, famous writers, seaside piers and the Rolling Stones tongue motif.

Pearce said he was shocked to get a call from the chancellor saying he had won.

“I heard about the competition through my design teacher at school and I thought I had nothing to lose so I decided to enter. I spent a lot of time researching what coin designs looked like and what sort of designs would represent all parts of the UK before submitting my idea and I honestly cannot believe I have won,” he said.

Osborne said last year that the threepenny bit shape was chosen in honour of the Queen, given that 12-sided coin was the first she appeared on. He said Pearce would now leave a “lasting legacy” with the new pound coin.

“The competition captured the imagination of thousands of people and David Pearce’s winning design will be recognised by millions in the years ahead,” said Osborne.

Over the past few years, around 2 million counterfeit £1 coins have been removed from circulation each year and the Treasury hopes the new secure coins will reduce costs to businesses and taxpayers.

The coin is the latest move in a battle against increasingly sophisticated counterfeiters. Last year the Bank of England announced it will introduce plastic, or polymer, banknotes from 2016 that are harder to copy. The change over will start with a new £5 note featuring Winston Churchill next year, and a Jane Austen £10 a year later.