British drivers can pay peanuts for their parking.

Three parking lots in Leeds and Manchester have started a program where drivers can pay for their spots with chestnuts – the dark brown seeds that fall off horsechestnut trees during the fall, the Associated Press reports.

"This fantastic, but slightly bonkers idea will raise the profile of Yorkshire Wildlife Trust's wonderful woodlands and hopefully raise a bit of cash to help us look after them," Jonathan Leadley of the Yorkshire Wildlife Trust told the BBC.

Town Centre Car Parks, the company running the "Bonkers for Conkers" program, initially ran it for a week but has since extended it longer, executive Ben Ziff said. The company is accepting the horsechestnuts also known as conkers – worth 20 pence (32 cents) each — to pay for parking. About 15,000 chestnuts have been collected so far which will be donated to Hetchell Wood Nature Reserve in Leeds.

The company outlined other “conker clauses” on their website:

1. One intact conker can be exchanged for parking at a value of 20 pence, up to a maximum of £10.

2. A maximum of 50 conkers can be exchanged per vehicle within the validity period.

3. Offer is only valid between Monday 16th September and Sunday 22nd September.

4. Offer valid at the following TCCP car parks: The Merrion Centre, Leeds, Clarence Dock, Leeds, and 30 Tariff Street, Manchester.

5. One vehicle per household can exchange conkers within the validity period.

6. The National Society for Prevention of Cruelty to Conkers forbids any conkers that have been used in competitions to be exchanged.

7. No cash alternative.

8. This offer cannot be used in conjunction with any other promotion or offer.

9. Town Centre Car Parks decision is final.

The chestnuts are only accepted by parking lot staff, not automated machines. "You can't put conkers into coin slots," company spokesman Matthew Williamson said.

The curious program has an environmental purpose. “Car emissions are on the rise throughout the country. We thought it would be a fun idea to raise awareness and give a little bit back,” Ziff said.