Fresh from negotiating a new deal with secretive Swiss banks, George Osborne has warned top earners who attempt to avoid tax that the government "will find you and your money".

Writing in the Observer, the chancellor reasserts his determination to ensure that the tax system is fair and says the clampdown announced on rich people sheltering their wealth in Switzerland is "just the start".

"Tax evasion is morally repugnant," he writes. "It's stealing from law-abiding people, who face higher taxes to make good the lost revenue."

Osborne's tough talk on tax comes amid Westminster speculation that the government is seeking to slash the 50p tax rate on the highest earners, and is seen by some as part of a campaign to soften the potential blow to the government's image.

It is understood that the Liberal Democrats are pushing for a "wealth tax" of some variety, possibly through a council tax superband on high-value homes, as a replacement for the 50p rate. Osborne, however, is said to be more keen on a series of high-profile but politically painless tax-avoidance measures like the deal with Switzerland. Under the agreement, UK accounts held in Switzerland in May 2013 will be subject to a one-off levy of as much as 34% of the contents.

Swiss authorities will then impose a "withholding tax" on British-held accounts that are not properly declared to HM Revenue and Customs. Approximately £100bn-£125bn of British investors' money is currently believed to be in Swiss banks.

"We've been working on this deal for over a year, and it will bring in potentially billions of pounds in revenue," Osborne writes. "It amazes me to hear that the last Labour government had the opportunity to do this a decade ago, but didn't. Just think of the billions of pounds that could have been collected and was instead left in the pockets of the tax cheats."

He adds: "We will make sure that everyone pays their fair share."

However, a senior Lib Dem source said he was unconvinced that the clampdown on tax avoidance would be enough to convince voters.

It emerged last night that there are divisions even within Conservative ranks over whether the 50p rate should be scrapped. The universities minister, David Willetts, said the symbolic importance of the top rate of tax should not be underestimated.

"It is very important that people see that when times are tough, we are, as they say, all in it together," he said. "That is an argument. People see that there are higher rates of tax being borne.

"That's why we have kept it so far. Because if you are expecting sacrifices from people with modest earnings it's right that that can apply to high incomes as well."

The taxing of the wealthy is also a matter of fierce debate in the US, where Warren Buffett, the billionaire investor, called for higher taxes from the rich to help bridge the country's massive debt gap, which stands at $14.3 trillion.

In France last week, an open letter by L'Oréal heiress Liliane Bettencourt, co-signed by 15 of her super-rich countrymen, called for higher but "reasonable" levies on "the most favoured" French taxpayers.