I actually had this conversation with SKy when considering switching to them myself. I was informed that authorized testing was 'probably' okay, but from their legal and contractual obligations 'anything' identified as malicious is a violation of contact and potentially result in loss of service.
From my knowledge of the ISP market in the UK ( and to a lesser extent, further afield) I'd be surprised if they had monitoring on the connections to this degree (or at least don't act on the information) and any investigation into violation of AUP is likely reactive, if and when a complaint is received. The price point of broadband in the UK doesn't make it cost effective for ISPs to be that proactive.
That said, the information that I received from them meant I personally went elsewhere for my network connection. Personally I don't want to have to explain to a client I can't fulfil a contract as agreed because my ISP has cut me off. You're 'probably' safe performing scans over Sky, but if your performing business level assessments and services, then you should be utilizing a business grade connection, the price difference isn't too extreme.
Hope this helps, (and let me know if you need a good business ISP

)