Good views, nearby shops and "peace and quiet" have all been used to calculate how much council tax homes should be liable for, the Tories have complained.
Details of the criteria were contained in an internal Government handbook related to a revaluation of properties in Wales, which has obtained by the party.
Spokeswoman Caroline Spelman warned they could be applied to houses elsewhere in the UK, creating a "punishing and cynical tax on people's quality of life".
But local government minister Phil Woolas accused the Opposition of scaremongering, saying they had created needless anxiety with a "complete disregard for the facts".
The 2005 documents from the Valuation Office Agency - which acts as council tax inspectors - were released in response to written Parliamentary questions.
In a pilot, they showed, mobile and park homes were given higher council tax bills for features such as "convenience of public transport facilities", "peace and quiet", "shop providing basic groceries", "pleasant views" and "good security".
Ms Spelman said: "This is proof that Gordon Brown has turned council tax into a punishing and cynical tax on people's quality of life by increasing council tax bills if you live near shops, near a bus stop, or live in a neighbourhood with peace and quiet.
"It is no wonder that the revaluation in Wales forced council tax bills to soar for so many homes. Northern Ireland is facing the same treatment from April, and I fear England and Scotland will follow."
She said home improvements such as kitchen units, bathroom suites, double glazing and central heating had been recorded by inspectors "to help drive up bills".
Read More
"It is deeply worrying that householders had to fill in intrusive questionnaires about every aspect of their property, with the veiled threat of a compulsory inspection of their private home if they resisted," she said.
