UPDATE 1-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

* Coca Cola HBC, Sports Direct and Mondi 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 topshare index, FTSE confirmed on Wednesday, after share priceslumps during a year beset with difficulties.

Serco has dropped 8.5 percent since the end of June afterthe UK government asked the police to investigate allegedfraudulent behaviour by Serco staff working on the outsourcer'scontracts.

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

Energy services firm John Wood Group is alsorelegated to the FTSE 250 mid-cap index, while Greekcoke bottler Coca Cola Hellenic, which switched primarylistings 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 HospitalsGroup, Entertainment One, convenience foodgroup Greencore and Partnership Assurance Group,while Anite, coal miner Bumi, JPMorgan IndianInvestment Trust, Salamander Energy and UtilcoEmerging 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.