An investigation is under way after a charity shop was plagued by fly-tipping.
Rubbish including catering waste and bottles has been dumped in the wheeled trade waste bin behind the RSPCA shop in King's Lynn.
When the bin was full, bags of rubbish have also been left behind the shop, on Norfolk Street.
But council officials are now investigating after an item which identified a business in the town was also left in the bin.
Volunteer Elena Anastasi said shop staff were used to coming in on Monday morning and finding they had been targeted.
'We've had ongoing problems for a very long time. Despite the fact we lock it, people force it open,' she said.
'However someone made a mistake and left their contact details on one of the pieces of rubbish.'
Fellow worker Marie Hayes, who is in her 80s and has been volunteering at the shop since it opened almost 30 years ago, added: 'We have to pay to have this emptied and people just come and dump stuff.' The shop, which is staffed by around 20 volunteers, raises money towards the running costs of the RSPCA's West Norfolk Rehoming Centre at Eau Brink, near Lynn.
It also helps people on low incomes to pay their vets' bills. Over the years it has been open, it has raised more than £1m.
As well as its problems with waste dumping, the shop has also been targeted by thieves.
Last week, a hand-made teddy bear made by Merrythought of Ironbridge, Shropshire, which was priced £30, was taken from a window display. Other items have also been stolen from the premises.
Miss Anastasi said: 'When these things happen it's a massive disappointment for us.'
West Norfolk council said the waste dumping had been reported to its waste management team.
A spokesman said: 'They have arranged for the shop's waste bin to be emptied free of charge on this occasion.
'They are currently undertaking an investigation based on what they have recovered from the dumped waste. We have prosecuted in the past for similar offences.'
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