Homeowners nearing the end of their mortgage deals are facing a double whammy of higher interest rates and huge property markdowns by surveyors, which are adding as much as £2,000 a year to the cost of a loan.

Brokers suggest borrowers shop round for better valuations amid evidence that switching lenders can produce a 10%-plus increase in what your property is valued at. The Royal Institution of Chartered Surveyors (Rics) said variations of 10% were usually “allowed”.

However, brokers are becoming more concerned about inconsistent valuations as lenders increasingly offer better rates to those with more equity in their homes. The average £200,000 loan at 75% of the property value is £85 a month, or £2,040 a year, cheaper than a loan at 90% as lenders shun “risky” applicants who have small deposits or less equity in their homes.

David Hollingworth of broker London & Country said: “Clients want valuers to provide consistent, realistic valuations. With more lenders introducing tiered rates it is ever more crucial.”

The Association of Mortgage Intermediaries (AMI) is calling for Rics to investigate “worrying fluctuations” in valuations from surveyors used by the biggest lenders.

Director-general Chris Cummings said: “Rics should be taking a stronger line with surveyors to make sure their valuations are within a tolerable range.

“Anything more than 2%-3% is a worrying trend in the current climate.”

Andrew Perez-Concepcion, 33, an office manager from Kingswood, Bristol, received three valuations on his home, which varied by more than 10% within two months. He initially applied to Nationwide to remortgage his £138,000 loan before his two-year fix expires at the end of this year.

Nationwide valued the property at £169,000 — £16,000 less than he expected — and offered a mortgage rate of 6.45%. Halifax further downvalued the property, at only £165,000, and offered an even higher interest rate at 6.49%.

The office manager then reapplied to Nationwide — and was stunned to receive a valuation at £185,000 — 9.5% more than its original valuation and up 11% on the Halifax price. That meant he qualified for a mortgage rate of 5.98%.

He said: “When Nationwide did the second valuation, it was the first time a surveyor actually came to the house.

“Different valuations meant we were facing an increase in payments of £43 a month. When everything else is going up too, it makes a hell of a difference."

Mark Ramsook, 28, of Surrey Quays, east London, a management consultant, experienced a similar problem. He was facing a £200 a month jump in mortgage repayments when he applied to Halifax for a £218,000 loan on his home.

He believed the property was worth around £320,000, but Colleys, the Halifax-owned surveyor, valued it at £275,000. That took the loan as a proportion of the property value to 79%, and would have added £100 a month to his monthly repayments.

However, Nationwide’s surveyor, Countrywide, valued the property at £310,000 — a 13% increase on the Halifax valuation — giving a loan-to-value of only 70%. “Applying to Nationwide saved me about £100 a month,” said Ramsook. “I was worried but it has worked out well in the end.”

A year ago, monthly repayments on a £200,000 loan at 90% of the property value worked out £27 cheaper than repayments on the same loan at 75% of the property value, according to Moneyfacts, the financial data firm. This is because lenders were offering cheap deals to those with small deposits in an effort to grab more of the market.