A 40-foot deep sinkhole that opened up in the middle of a popular Wooburn playing field amid recent heavy rain is getting even bigger.

The massive hole opened on the site of a former brickworks which was filled in by army engineers to create a recreational area.

Shocked dog-walker Lesley James, 50, was stopped in her tracks when she came across the massive hole in the grass on Saturday.

She said the hole, in the middle of Sappers Field was only three or four feet across - but described it as like a "cavern" in depth.

The six-acre field was created by a group of Royal Engineers on the site of an old council landfill which had featured a number of old wells.

Lesley, who lives six miles away in Marlow, but is temporarily staying in Wooburn Green, said: "I thought it was a large rabbit hole at first.

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"It was only when I went right up to it that I saw how much the ground has given way.

"It was a bit scary, because I didn't know if there was anything underneath where I was standing.

"I could see that the ground was stable on the other side, because I could see a ridge supporting it - but I thought, 'Oh god, what if I'm standing on nothing?'."

Lesley added: "Luckily me and the dog were the only ones in the field at the time.

"I put a wooden pallet over the top of the hole to warn other people, until the experts came along."

Lesley said she had "no idea" what may have caused the sinkhole to open up, but said it may have given way after all the recent rain.

And the sinkhole only appeared to continue to grow as staff from Wooburn and Bourne End Parish Council arrived to inspect it.

The parish council was left with no choice but to cordon off the whole park, which is a popular playing field and dog walking spot, until it can come up with a solution.

It also hopes to install security fences around the hole.

Parish councillor Malcolm Silver said the sinkhole is continuing to grow - and that it will take a "long, long time" to fix it.

He said the council has no certain idea of what caused it, but added: "The site was originally a brickworks, and after the war it was filled in by sappers - soldiers who did not have jobs.

"However, there is running water underneath it, and we think that over time that water has washed away all the stuff used to fill in the site.

"There is now a big cavern under the field - which is today used as a park, with a football field and playground.

"We think it is now bigger than 40 foot deep. We threw something down it to see how long it would take to hit the bottom, and it took three seconds - so it is definitely growing.

"It's probably a combination of the recent wet weather and the fact there were three old wells on the site that has led to the sinkhole."