Tax amnesty on undeclared income

A client contacted me yesterday and told me that he wanted to get some undeclared income sorted out. He has an overseas property, the rental income from which has been paid into a Swiss bank account which goes back a number of years  and none has been remitted to the UK. He is UK resident and ordinarily resident but not domiciled although he hasn't taken advantage of the £30,000 payment to retain his non domicile. I know there was an amnesty granted some time ago for undeclared Swiss bank accounts although this expired but apart from coming clean is there anything he can claim in respect of that amnesty or anything else that would mitigate his tax and penalty or is this something that would benefit from specialist advice. Although I've dealt with normal HMRC investigations I've never had anything like this.

Thanks