A new army of council tax 'inspectors' is to be given the right to enter people's homes and issue fines to anyone who refuses to cooperate.
Camera-wielding officials will be able to take photographs inside properties, including bedrooms, and rule they should pay more if they have home improvements such as patios and conservatories.
Residents could be fined £1,000, and then £200 every day after that, if they do not let the inspectors in or fail to properly 'assist' them.
The Conservatives branded the proposals a snoopers' charter that would trample over fundamental civil liberties.
Homeowners are expected to face higher council tax bills if they enjoy good views or have improved their property by building an extension or putting in double glazing.
Under a new house price tax, 'site positive' features would include gardens, patios, conservatories, double glazing, scenic views, number of bedrooms and number of parking spaces.
Shadow local government secretary Caroline Spelman said legislation being discussed in Parliament today would pave the way for council tax inspectors to have new powers to enter and assess properties.
In an alarming addition, residents who 'fail to give reasonable assistance' or do not cooperate with the inspectors will be fined £1,000 and be recorded on local police and court records.
If the householder continues to obstruct, hinder or fail to provide assistance, they can be fined £200 per day on top, she said.
The Tories claim ministers are quietly introducing the new scheme in Northern Ireland before rolling it out nationwide, just as Margaret Thatcher piloted the community charge in Scotland before introducing it in England and Wales.
Shadow Local Government Secretary Caroline Spelman said: "Northern Ireland is now being used as a testing ground for Gordon Brown's tax inspectors, from the levying of a new house price tax, to the use of invasive Big Brother computer databases, to new aggressive state powers to enter family homes.
"Labour craves these powers since they want to tax every feature of people's homes - including bedrooms, conservatories, double glazing and garden sheds.
"For all of Labour's talk of human rights, these new powers are the footprint of an oppressive and greedy government.
This tax will hit Northern Ireland in April, with a Government review of town hall finances thought to be looking at the same system for England.
The Conservatives warned that if introduced in England, average bills would go up by £436 a year, with middle-class households in the South and South East worst hit.
If the Northern Ireland model was applied in England, several councils - including Westminster, Wandsworth, Camden, Hammersmith and Fulham, Richmond upon Thames, Islington, South Bucks, Windsor & Maidenhead, Mole Valley, St Albans, Winchester, Brentwood and Epping Forest - would see average annual bills rise by more than £1,000.
In many Labour heartlands, by contrast, average bills would fall because house price rises have been less dramatic since the last national revaluation.
A spokesman for the Department for Communities and Local Government accused the Tories of "scaremongering" and said the measures only applied in Northern Ireland.
"The Government is not using Northern Ireland as a testing ground. It has a different system of local government finance from England.
We in Northern Ireland are going to get well and truly ripped off again but it's OK since we will still be retaining the eleven plus!!
