(1) In determining for the purposes of this Chapter what part of the taxable value of a gift or inheritance is attributable to the value of relevant business property so much of the last-mentioned value as is attributable to - 

(a) any excepted assets within the meaning of subsection (2), or

(b) any excluded property within the meaning of subsection (7),

shall be left out of account.

(2) An asset shall be an excepted asset in relation to any relevant business property if it was not used wholly or mainly for the purposes of the business concerned throughout the whole or the last two years of the relevant period, but where the business concerned is carried on by a company which is a member of a group, the use of an asset for the purposes of a business carried on by another company which at the time of the use and immediately prior to the gift or inheritance was also a member of that group shall be treated as use for the purposes of the business concerned, unless that other company's membership of the group falls to be disregarded under section 133:

Provided that the use of an asset for the purposes of a business to which section 127(4) relates shall not be treated as use for the purposes of the business concerned.