Dad Tim made the gruesome find and managed to trap the spider by ne of its long legs using a bowl.
The spider was reportedly six-inches long and, after looking it up online, Tim and his wife Lisa found out it was a Brazilian Wandering Spider.
Speaking to the Daily Mail, Tim said: "We were terrified. We got ourselves and our kids out of the house straight away."
Once he, Lisa and their sons, aged seven and eight, were safe, Tim called the RSPCA to come and remove the arachnid – but they allegedly told him they 'weren't equipped to deal with such a spider'.
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Eventually, after even the police refused to help, a Waitrose worker had to catch the spider. But when he went inside, accompanied by Tim and Lisa, they discovered it had ripped its own leg off to escape.
Tim continued: "We had no idea where it had gone."
After they discovered a 'bulging' egg sac – which could have contained hundreds of babes – Waitrose sent in a pest expert.
Thankfully the expert managed to catch the spider – it is believed to have been taken to a centre abroad – and dispose of the eggs.
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"Although people think these things are funny, I keep thinking that the spider could have killed me or my son if he had gone to get a banana," Tim said.
Waitrose gave the family £150 worth of shopping vouchers as compensation, and said: "The safety of our customers is our absolute priority.
"Although this is highly unusual, we're taking it seriously and will be working with our supplier to minimise the risk of this happening again."