Though first past the post might wipe out the Tories in the Scottish Parliament and Welsh Assembly, it could deliver gains to them in the London-wide elections.
Shadow local government minister Nigel Waterson said: 'We wouldn't abolish [devolution] if that's what people want, but I think we should stay with the tried and tested British voting system.'
The Tories are likely to include a 'free councils' policy in their manifesto. This would reward successful councils with more autonomy.
Mr Waterson said: 'Councils that have a proven track record of delivering cost-effective services of a high quality can produce a business plan, submit it to the secretary of state and say how they want to run the council.
'They would have rather more freedom than other councils in terms of actions, and also they'd be able to raise bond issues for particular projects and spend money on things that ordinary councils wouldn't necessarily be licensed to do.'
Local Government Association chairman Sir Jeremy Beecham said: 'It's the old Tory story of more freedom to do less, given that their policies in education, social care and housing would scale down the role of local government very significantly.'