Serco, ENRC demoted in reshuffle of Britain's FTSE

* Serco leaves Britain's top index after five-year stay

* ENRC and John Wood Group also leave FTSE 100 (FTSE: ^FTSE - news)

* Coca Cola HBC, Sports Direct and Mondi (LSE: MNDI.L - news) make FTSE debuts

* Reshuffle implemented after market close on Sept. 20

By Alistair Smout

LONDON, Sept 6 (Reuters) - Outsourcing firm Serco and Kazakh miner ENRC will both leave Britain's top share index, FTSE confirmed on Wednesday, after share price slumps during a year beset with difficulties.

Serco has dropped 8.5 percent since the end of June after the UK government asked the police to investigate alleged fraudulent behaviour by Serco staff working on the outsourcer's contracts.

Kazkh miner Eurasian Natural Resources Company is down 22.2 percent year to date, and leaves the index just as its founders finalise plans to take it private after six years in London, marred by corruption probes.

Energy services firm John Wood Group is also relegated to the FTSE 250 (FTSE: ^FTMC - news) mid-cap index, while Greek coke bottler Coca Cola Hellenic, which switched primary listings from Athens in April, will join the FTSE 100, along with two other debutants, retailer Sports Direct and packaging firm Mondi.

Earning promotion to the FTSE 250 are Al Noor Hospitals Group, Entertainment One (LSE: ETO.L - news) , convenience food group Greencore and Partnership Assurance Group, while Anite (LSE: AIE.L - news) , coal miner Bumi, JPMorgan Indian Investment Trust, Salamander Energy (Other OTC: SALDF - news) and Utilco Emerging Markets all lose their mid-cap status.

The changes are implemented after market close on Sept. 20, taking effect at the start of trading on Sept. 23.