The Trustee Powers
Trustees have various powers which are given to them by law, mainly the Trustee Act 1925 and the Trustee Act 2000. These powers are often added to, varied or restricted in the Trust Instrument. We're going to look at the power of maintenance, which is s.31 Trustee Act 1925 and the power of advancement, which is s.32 Trust Act 1925.
Power of Maintenance
This power enables the Trustees to spend income (but not capital) for the benefit of beneficiaries who are under the age of 18. This is a discretionary power, in other words the Trustees do not have to advance the income to the beneficiary but they have the sole discretion to do so "in all the circumstances, be reasonable". Any income that is not applied is accumulated.
This power applies whether the gift to the beneficiary is contingent (i.e. payable upon a certain event happening, such as attaining the age of 21 or 25) or vested (an absolute gift).The income available for maintenance payments is only that income which arises on the property to which the beneficiary is or will be entitled to.
The Trustees shouldn't automatically pay the income to the beneficiary just because the power allows them the discretion to do so. Before paying any income for the maintenance of the beneficiary, it is important that the trustees ascertain what the payments are for and whether there is any income available from an alternative source for the same purpose. In Wilson v Turner  the Trustees paid the income to the infant beneficiary's father automatically without inquiring as to the beneficiary's actual needs, and the father's estate was required to repay the money.
Once the beneficiary attains the age of 18, he becomes automatically entitled to any income arising and the Trustees must pay this to him.
This power can excluded by the Settlor who can direct instead that the income should be spent on someone else or accumulated within the Trust.
Power of Advancement
This power allows the Trustee to advance capital of the Trust Fund for the benefit of the beneficiaries. Once again, this power applies whether the gift to the beneficiary is contingent (i.e. payable upon a certain event happening, such as attaining the age of 21 or 25) or vested (an absolute gift). This means that a beneficiary could receive some or all of their inheritance despite not satisfying the contingency applied to the gift unless this is expressly excluded within the Trust Instrument.
This again is a discretionary power, in other words the Trustees do not have to advance the income to the beneficiary but they have the sole discretion to do so "in all the circumstances, be reasonable". Though, S.32 Trustee Act 1925 limits the amount to be advanced at one half of their share, however, this can be edited so that the whole share can be advanced.
Trustees do have an obligation to see that the money advanced actually goes to benefit the beneficiary. In Re Pauling's Settlement Trusts  large sums of money were advanced and the Trustees were aware that it was being spent by the beneficiaries' father on the family's living expenses. The advancements were therefore held to be in breach of the Trust and the Trustees were required to repay the money. The Trustees could not advance money 'without any responsibility .... even to inquire as to its application'. In practice, it is sensible for the Trustees to pay the money directly, such as directly to the garage if a car is being purchased or to the Solicitor if it is intended for a deposit on a property.
It is worth noting, that both sections 31 and 32 Trustee Act 1925 are modified when the STEP Standard Provisions (1st or 2nd Edition) are included within the terms of the Trust Instrument.