Are we talking about individual contractors (aka "agency technicians")?
Competency (or otherwise) is generally apparent on the first working day. The Trust (if it has any sense) should reserve the right to have the contractor removed if necessary.
However it should not be too difficult for someone to pick up a 'phone (or tap out an email) to "check out" an individual contractor (assuming he has done work for the NHS in the recent past) before taking him on.
The contractor should be supervised (at least nominally) by an appointed member of the permanent staff (eg, Senior Technician, EBME Manager etc.). It may be prudent to have the fact that a contractor is being used for specific tasks entered on the Trust Risk Register.
On the other hand - if my own experiences are anything to go by - sometimes a contractor may be "badly briefed" (misled about the nature of the work); neither is it unknown for the contractor to be expected (required) to work in conditions that permanent staff would not even consider (I'm thinking "Health and Safety" here).
I have many stories, but I suspect you get the picture!
Don't forget that the "company" will be represented by a (silver tongued) sales type; the actual person sent along to carry out the work will be someone else entirely. Unless, of course, we are talking about a "self employed" - or freelance - person (but, sadly, I have never heard of any NHS folk hiring such a person for EBME work directly).
In short, where contractors are involved, there is always a contract (believe it or not); it is at that stage (the signing of the contract) when all this stuff needs to be dealt with.
