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* Clearing customers could leave if no clear Brexit path
* Clearing, ancillary services jobs at risk
* Existing rules should stay in place until 2022 - Rolet
By Huw Jones and Andrew MacAskill
LONDON, Jan 10 (Reuters) - Tens of thousands of jobs inBritain's financial services sector could be lost if euroclearing shifts to continental Europe and full access to thebloc's single market is lost, top industry officials said onTuesday.
London has become the world's biggest centre for clearingeuro-denominated financial contracts, and some continentalpolicymakers want this shifted to the euro zone after Brexit.
Xavier Rolet, chief executive of the London Stock ExchangeGroup, owner of the world's biggest clearing house foreuro-denominated contracts, said that without clarity on whathappens to markets after Brexit, clearing customers in Londonwill leave.
Some tens of thousands of jobs could leave London, not justfrom clearing itself, but also from ancillary services likesoftware and IT, risk management, and administrative staff,Rolet told parliament's Treasury Select Committee.
To avoid customers quitting London when Britain beginsformal divorce talks with the EU in March, existing rules shouldstay in place until 2022 to avoid disruptions that couldundermine financial stability, Rolet said.
Already, banks with large London operations say they willstep up lobbying European officials because they are running outof arguments to convince the British government the industryneeds single market access.
Douglas Flint, chairman of HSBC bank, told thelawmakers that banks without operations elsewhere in the EU willlikely trigger migration plans immediately after EU divorcetalks begin in March, estimating that "tens of thousands" ofjobs are linked to EU "passporting" rights.
Currently, banks have passporting rights, allowing them tooperate across the 28-nation bloc from a base in Britain. Theycould lose this right under Brexit.
Possible job losses in banking would depend on how lendersin Britain negotiate new licences with regulators on thecontinent, raising question marks about the back office staffacross Britain's regions.
This could hit JPMorgan, Citigroup andDeutsche Bank which currently employ thousands ofback-office staff in regional cities around Britain in placessuch as Bournemouth and Glasgow.
"Clearly you would need to move the front part of thebusiness," Flint said. "The question would be whether thenegotiation would allow the middle and back office, thesettlement, the risk management, the accounting and so on to bedone out of the EU 27."
Rolet said that since Britain's referendum on the EU, he hasheard of calls made by continental European regulators tocustomers, warning them of the risk of euro clearing leavingBritain.
"That resulted in commercial pressure on our business,"Rolet said.
The EU is reviewing its derivatives trading and clearingrules which could include ways to making it impossible to cleareuro-denominated contracts in the UK, Rolet said.
"Those sort of pesky, well-targeted, seemingly minorregulations that actually have a major impact on customerbehaviour."
It would amount to an effective control on currencies in theEU and backfire on the bloc, he added.
Flint, Rolet and Allianz Global Investors Vice ChairElizabeth Corley appearing before the lawmakers all said atransitional deal would need to last until at least 2021 toallow companies enough time for a smooth departure from the EU.
Flint said one of his biggest concerns is that by Britainleaving the EU the regulatory rules that have converged in thedecade since the start of the global financial crisis risk beingfragmented, undermining economic stability.
"After 10 years of putting it in place it would in my view,be seen with hindsight, as one of the worst actions that couldhave ever taken place," Flint said. (Reporting by Huw Jones and Andrew MacAskill, editing by SusanThomas)
