I would have to look it up, but, yes we have had retrospective legislation, which caused plenty of problems, one currently being reviewed would go back to pre-9/11 regarding anti hoaxer laws about bio-terrorism.
It seems such a specific law that it is designed to catch known persons who have been using a loophole, I’m not sure it will survive the European Courts should it be appealed that far.
Another is having suspects on US arrest warrant be liable for deportation for things that were not regarded as an offence in this country, normally if something is not an offence in the UK, then you cannot be extradited to another country to face criminal proceedings for it, and if it is an offence in the UK, then extradition can only take place if there is a prima facie case against the extraditee, this law proposes to extradite persons only on accusations and does not require an actual indictment by the US.
It appears to be a convenient way for the UK to get rid of individuals such as Abu Hamsa, who we don’t really want over here, but we don’t have any evidence of criminal activity to remove him.
In his particular case, if the US did indict him, we could not extradite him because the charges could potentially unravel out to terrorism charges which could attract a death penalty in the US, and under European Act we cannot do this as under Article 1’ Every person has the right to life’
Now if he is merely a suspect, but not indicted, for activity prior to the law being enacted, he is not technically under death penalty threat, so he could be sent to the US and we would have rid of him.
I notice the US does not see fit to do the same with Irish Terrorists historically.
http://www.sovereignty.org.uk/siteinfo/newsround/passport.html
I know that some legislation for Health and Safety issues have had the injury reporting times extended prior to when some laws were enacted.
…and to add to Giles comment, there are two other ways laws can be enacted in the UK, one is through legislation handed down through the European Executive, which requires a particular standard to be met in local national law within a certain period decided by the executive itself.
The other way laws can be enacted in the UK is through authority embodied in an agency for that purpose- and can include employment law too.
The best known to most people would be the Heath and Safety Commission, which has the power authorised by the Home Secretary to make laws affecting such matters and these do not have to be reviewed through Parliament.
Other agencies that can make law in this way are Environmental Agency, this is called secondary legislation, the primary legislation being the one that set up and authorised the agency in the first place.