The average monthly interest rate offered by U.K. lenders on two-year, fixed-rate mortgages funding 75% of a property's value rose in September to the highest this year, according to data released Friday by the Bank of England.

The average rate was 4.46% last month, up from 4.43% in August and 4.42% in July. The rise pushed the rate to its highest since it was 4.77% last December.

The data suggests the current upturn in the housing market should be treated with caution and that lenders are struggling to keep loan costs low despite the Bank of England's benchmark interest rate's remaining unchanged at a record low 0.50% since March.

The data also showed that the average standard variable-rate mortgage was unchanged in September, at 3.93%. It remains a little above the all-time low of 3.82% in April and much lower than the recent peak of 6.95% in September 2008.

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