Power of revocation or variation

(1) A trust and any exercise of a power or discretion under a trust may be expressed to be capable of revocation, in whole or in part, or of variation. (2) No such revocation or variation shall prejudice anything lawfully done by a trustee in relation to the trust before he receives notice of the revocation or variation. (3) Subject to the terms of the trust, if a trust is revoked in whole or in part, the trustee shall hold the trust property, or the part of the trust property which is the subject of the revocation, in trust for the settlor absolutely or, if he is dead, as if it had formed part of his estate at death. (4) In so far as the terms of a trust make no provision for revocation of the trust, then the trust shall be irrevocable.