The Lib-Dems believe their new tax bands will raise about £1.5 billion when levied against properties now worth £2 million and above.
The party has refused to be drawn on how the policy would work, but one senior Lib-Dem has suggested it could be hugely complicated.
A senior party figure last night suggested that the new higher bands would have to be based on a property’s notional value in 1991 to fit with the current system.
The existing bands were set that year and governments have failed to update them since then, fearful of a backlash from voters facing tax hikes.
Properties that were worth £320,000 or more are currently placed in the top valuation band for council tax, with residents of homes of all values above that paying the same rate.
The council tax bands plan comes after the Lib-Dems ditched a proposal for a Mansion Tax on all homes above £2million, now favoured by