MiFID requires that you are giving your client best execution.
http://www.fsa.gov.uk/Pages/About/What/International/EU/fsap/mifid/index.shtml
http://www.exchange-handbook.co.uk/articles_story.cfm?id=54127
Section 4.29 states that CDS (single name and tranches) come under the requirement
http://www.fsa.gov.uk/pubs/discussion/dp06_03.pdf
although section 4.39 indicates that equities will require the most transparency.
The following link appeared on ContractorUK today
http://www.contractoruk.com/news/002671.html