Controversial tax refund firms are taking hundreds of pounds worth of HMRC rebates from households by helping to claim them, experts warn. The unregulated firms are controversial because they take a slice of cash owed to people when they could easily claim back the tax for free. Some firms use tax calculators to collect personal information, which once on file can be used indefinitely to make claims. Experts warn that people can unwittingly start a claims process when using these tools without knowing it.