What's wrong with the Herks??
Seriously, the CAA has no power to stop foreign registered aircraft flying into UK airspace as long as they are registered in an ICAO contracting state. Foreign registered aircraft are the responsibility of the UK Government (through the Department of Transport). It is the Dept of Transport that gives permission for foreign operators and aircraft to fly into the UK.
The only aircraft that have been banned are due to noise regulations (which are EC
laws) and some African states that are not considered to meet international standards (I believe it currently includes aircraft registered in Congo and Sierra Leone), along with some individual operators.
The CAA does carry out ramp checks and audits of foreign operators, but only at the request of and on behalf of the Dept. of Transport.
As the Algerie Herks meet noise regulations, and are registered in a contracting state, there is no reason why they shouldn't fly into the UK for many years to come!