HM Revenue & Customs has removed all but three Canadian pension schemes from its list of Recognised Overseas Pension Schemes (Rops).
The tax office offered no explanation as to why it had removed 49 schemes from the list.
A spokesman for HMRC said: "We don’t comment on identifiable jurisdictions."
The sudden move follows a similar cull of Australian Qrops from HMRC's list last year.
According to Montfort International managing director Geraint Davies, who is a financial planner specialising in expatriates, the sudden removal of most Canadian schemes from the list could leave many expats liable to a 55 per cent tax charge.
He said it suggested HMRC had been investigating the Canadian schemes and found they were not compliant with UK pension law.
In particular, he said Canadian law allows pension policyholders to withdraw their funds before age 55 under certain circumstances, including when they are suffering financial hardship or are permanently emigrating.
Mr Davies said he had expected the removal of Canadian schemes and therefore did not advise his own clients to transfer to a pension based in this country.
However, he warned that some advisers may not be doing their due diligence, therefore exposing their clients to a significant tax risk.
Mr Davies blamed the way the HMRC list is compiled.
He said: "You tell HMRC that you meet the conditions, and they put you on the list. There are two ways a scheme comes off the list. Either you self-assess as not meeting the conditions, or HMRC determines that you don't meet the conditions."
Mr Davies said it seemed clear the latter had happened in this case, though he added: "HMRC won't say anything. They won't comment on the reasons for it."
Given HMRC's apparently hands-off approach, Mr Davies said investors face two risks. The first was from unscrupulous providers who simply want to "flog a product without understanding the compliance demands".
He warned that this was a major risk, stating: "I would suggest that most countries have not done their due diligence."
The second risk to investors came from financial advisers who were "not doing the research they should be doing in this complex area", Mr Davies said.