detasman nije bas hrvatska rijec, tj. posudjenica je iz francuskog, a cula sam je samo par puta na starim pre-90ies vijestima, obicno u svezi s vojskom.
http://www.kombeg.org.yu/pdf/detasman.pdf

in general terms that's a temporary work relocation, or in some companies "international work assignment" or in the UK Intra-Company Transfer

An Intra-Company Transfer work permit (ICT) is applicable for the transfer of key staff into a UK subsidiary company.
http://www.ukmigrationvisas.com/intra-Company-transfers.php

http://www.birkettlong.co.uk/Services-for-Business/business-...

I used to work in the relocation industry, and the only thing that comes to mind is something of the sort, depending on how detailed a translation you need.
try checking out the UK govt. pension pages (I think I also saw something there about pension contributions when working abroad for your company, or something of the sort)

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Note added at 41 mins (2008-04-20 12:06:59 GMT)
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just a brief expl. regarding "detasman" - you are an employee of a multinational firm, hired and with a contract in Croatia, but at a certain point your company (or govt. or institution) needs you somewhere else, because of your skills, capabilities. this is only for a certain period of time (countries will issue visas/permits for this generally up to a max of 5 years, e.g. UK, Italy). During this time you will still be paid by your "mother company", i.e. the Croatian branch, and your pension fund money will still be paid by the Croatian company to the croatian pension fund. You do work in the UK, but you are still an employee of the Croatian branch.