Review of contracts is expected to be completed in time for its annual results

Embattled outsourcing group Serco warned it would have to write down the value of several big contracts relating to asylum seekers' accommodation centres and clinical healthcare, after new boss Rupert Soames embarked on a review of the business. The move could harm annual profits, although for the time being the firm is sticking with previous guidance.

The company has become mired in a series of scandals and recently disclosed that 10 of its staff had been fired in relation to allegations of improper sexual contact with female detainees at the Yarl's Wood immigration detention centre.

Soames said: "Whilst difficulties continue on some contracts, overall our trading and financial position is in line with the expectations on which we updated the market two months ago. We are rebuilding trust and confidence with the UK government and the strategy review is proceeding according to plan."

Serco still expects to make adjusted operating profits of at least £170m at constant currencies, with adjusted revenues flat at £2.4bn in the first half of the year. The company won more than £2bn of contracts during that time.

However, it flagged up likely further writedowns of £10-15m for its Compass asylum seekers' accommodation centres and clinical healthcare contracts, which could affect its stated profit expectations.

Serco's review of its lossmaking contracts such as Compass – which has lost £15m so far and is still losing money – is expected to be completed in time for its annual results. It also had to write down its underperforming UK clinical healthcare contracts by £18m last year.

Serco, often described as the "biggest company you've never heard of", runs a host of government and other services in Britain and around the world, such as rail franchises, prisons and school inspections. It has come under fire for providing "substandard" services over the past year, has seen its stock market value slump and been cast out of the FTSE 100 index.

As private involvement in the NHS grows, Serco has won a number of healthcare contracts, such as running out-of-hours GP services in Cornwall. The service was damned by the House Of Commons public accounts committee which found Serco had replaced clinicians out of hours with call-handlers without medical training.