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Aviva chief executive Mark Wilson will walk away with a pay and benefits package of up to £6.5m when he leaves the insurance company next year.

Announcing Mr Wilson's surprise departure, the firm said it was "time for new leadership to take the group to the next phase of its development".

He will step down from his role immediately but stay with the group until April to help the transition.

Aviva said its aims under Mr Wilson's leadership had been achieved.

His package includes a minimum of one year's salary, three years of annual bonuses, legal fees and other benefits.

Mr Wilson was appointed in January 2013 and since then, the company's financial performance has significantly improved.

The company said it would immediately start looking for Mr Wilson's successor and that non-executive chairman Sir Adrian Montague would assume executive responsibilities in the meantime.

Sir Adrian said: "Mark leaves the group in a far stronger state than when he joined.

"There is much further to go in accelerating our strategic development and enhancing shareholder value. We have agreed with Mark this is the right time for a new leader to ensure Aviva delivers to its full potential."

Mr Wilson said the company was in "poor health" when he joined it and added: "I am happy I leave the company in a strong position from which it can thrive."

Aviva's share price rose by 2% in early trading after the news of Mr Wilson's departure was revealed.

In March this year, Aviva scrapped controversial plans to cancel £450m of high-performing preference shares.

The proposal had been met with an angry response from investors and after reversing its decision, the company said it had acted after hearing views which included "strong feedback and criticism".

In the same month, there was more anger when Mr Wilson agreed to take a seat on the board of BlackRock, the world's biggest fund manager.

Analysis: By Dominic O'Connell, Today business presenter

Mark Wilson was one of the City's rising stars, tipped variously as the next chief executive of Royal Bank of Scotland, HSBC or any number of other giant financial institutions.

He took over Aviva at a low point - it had languished under his predecessor, Andrew Moss - and his common sense and speedy reforms set it on the road to recovery.

But he made a bad call in backing an attempt to redeem the company's preference shares - a form of share that guarantees its holders a generous rate of return in perpetuity. Aviva found a legal loophole to cancel the shares, drawing hefty criticism. Eventually the board was forced into an embarrassing climbdown.

In Aviva's statement there are clear hints that this is not a planned change of the guard, but an abrupt decision.

The company does not have a replacement in place, and chairman Sir Adrian Montague will take on executive duties. There is also talk about it being time for "new leadership for the next phase of development", a standard City euphemism for a face that no longer fits.

A successor will be sought inside and outside the company, but the bookies' early favourite will be Andy Briggs, already at Aviva as the boss of its UK insurance division.

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Neil Wilson, chief market analyst at trading company Markets,com, said his namesake's leadership at Aviva had been perhaps "looking a little stale, although the sector has been under pressure".

He said that the morning's rising share prices were "a bit of a kick in the teeth" for Mr Wilson, but added "overall you have to say that Wilson achieved quite a lot for the company, even if he is not the man to take it forward from here".

The Aviva name was first used in the summer of 2002, changing the name of the group from CGNU, which it adopted following the merger of CGU and Norwich Union two years earlier.

The company offers a wide range of insurance and savings products, including car and home cover and pensions.