I have heard the nurses were needed. Also the skilled building related trades: plumbers, tiler, electricans...
Unlikely as they were getting rid of nurses and employing more managers. Those that entered the "nursing profession" mostly were doing jobs the UK nurses felt were beneath them. Use your imagination. Electricians for sure would not be employable without certification as Polish standards are considerably different to the UK's. Can't comment on plumbers although having stayed in a Polish house where the toilets flushed with hot water , possibly standards differ with this profession also :-)
IMO immigration was used to drive wages down in the UK which it has succeeded in doing which can be gauged by youth unemployment. Where agency jobs were filled by our younger generations, they are now filled by Poles in their mid thirties. I know thats generalising but I believe it is about right.
Our potatoes were being picked
Now I was doing this aged 12, many years ago. Kind of confirms my point as you don't see teenagers doing it nowadays.