It's a bit of a thorny issue, I believe. One of my exes owned a temping agency so I did quite a bit of it at the time. Most of the places I worked at employed almost exclusively temps - many of whom had been working at the same place for years and years - mainly cos they can avoid paying SSP, holidays, etc. It's not necessarily a question of not wanting the permanent contract - it's down to whether the company concerned will give you one

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Oh, and not everywhere pays temps more - some pay less, some the same and some a little more. Depends on the company again.