We, in common with virtually all other companies, need to use estimates in the preparation of our financial statements. The most sensitive estimates affecting our financial statements are in the areas of assessing the level of interconnect income with and payments to other telecommunications operators, providing for doubtful debts, establishing fixed asset lives for depreciation purposes, making appropriate long-term assumptions in calculating pension liabilities and costs, making appropriate medium-term assumptions on asset impairment reviews and calculating current tax liabilities on our profits.

We are required to interconnect our networks with other telecommunications operators. In certain instances we rely on other operators to measure the traffic flows interconnecting with our networks. We use estimates in these cases to determine the amount of income receivable from or payments we need to make to these other operators. The prices at which these services are charged are often regulated and are subject to retrospective adjustment. We use estimates in assessing the likely effect of these adjustments.

We provide services to over 21 million individuals and businesses, mainly on credit terms. We know that certain debts due to us will not be paid through the default of a small number of our customers. We use estimates, based on our historical experience, in determining the level of debts that we believe will not be collected. These estimates include such factors as the current state of the UK economy and particular industry issues.

The plant and equipment used in our networks is long-lived with cables and switching equipment operating for over 10 years and underground ducts being used for decades. The annual depreciation charge is sensitive to the estimated service lives we allocate to each type of asset. We regularly review these asset lives and change them when necessary to reflect current thinking on their remaining lives in light of technological change, prospective economic utilisation and physical condition of the assets concerned.

We have a commitment, mainly through the BT Pension Scheme, to pay pension benefits to approximately 376,000 people over the next several decades. The cost of these benefits and the present value of our pension liabilities depend on such factors as the life expectancy of the members, the salary progression of our current employees, the return that the pension fund assets will generate in the time before they are used to fund the pension payments and the discount rate at which the future pension payments are discounted. We use estimates for all these factors in determining the pension costs and liabilities incorporated in our financial statements.

In the 2002 and 2001 financial years, we have made charges for the impairment of the carrying value of goodwill, investments and tangible fixed assets in our balance sheet. The amount of the charges are in most cases based on the discounted present value of the future cash flows that we expect to be derived from these assets. We use estimates in determining these future cash flows and the discount rate.

The actual tax we pay on our profits is determined according to complex tax laws and regulations. Where the effect of these laws and regulations is unclear, we use estimates in determining the liability for the tax to be paid on our past profits which we recognise in our financial statements.