overseas charity trading in UK

S506 TA 1988 defines a charity as a "...body of persons or trust established for charitable purposes only.".
If an overseas charity trades in the UK will they be able to claim exemption from UK income tax and or corporation tax under S505 TA 1988 on the same basis as a UK charity? If so does HMRC define which types of overseas charities they will recognise as eligible for such an exemption?
bernard gross