HBOS has become the fourth UK lender in a week to announce a multi-million pound writedown on the back of the turmoil in global credit markets, taking the total written off by UK banks in the last seven days to almost £2bn (€2.78bn).

The bank this morning said it wrote down £520m on its investments, three days after Lloyds TSB revealed a £200m hit on its own portfolio and a week after Royal Bank of Scotland reduced the value of its assets by £950m as a result of its exposure to US sub-prime.