The Supreme Court's unanimous ruling that employment tribunal fees are unlawful could lead to large numbers of old cases resurfacing, according to employment lawyers.

The Supreme Court ruled in favour of public services trade union Unison that the government had acted unlawfully when it introduced tribunal fees in July 2013, and said that the fees should end immediately.

The ruling means the government will have to refund thousands of people who paid to make tribunal claims during the four-year period.

Some lawyers believe that while the refunds are a welcome response from the government, potential claimants could now come forward who have previously been deterred by the fees associated with employment tribunals.

Lewis Silkin employment partner Colin Leckey says: "Most employment claims have to be brought within three months of the act being complained of. What we could see now is claimants who are not eligible to be refunded by the government because they did not bring forward a claim, but argue they would have but for the existence of the fee regime."

This is a view shared by other partners, who say that the lack of provision for 'retrospective claimants' coming forward could cause problems.

Irwin Mitchell employment partner Alan Lewis argues: "There is no doubt about it that tribunal claims will increase. If you had a claim worth £190, why would you spend twice as much and risk not getting it back in a tribunal? What will be interesting is that people will now come forward because the fees have proven to be unlawful. It could lead to a rise in out-of-date, retrospective claims that there is no plan for."

The role unions may play in bolstering support for retrospective claims could also exacerbate the issue, according to head of the international employment practice at Paul Hastings, Suzanne Horne.

She suggests that paying back fees to claimants is merely the "tip of the iceberg" and that a bigger issue will be "lower paid potential claimants, turned off previously by exorbitant tribunal fees, entering the fray with union backing".

Other partners highlight that the judgment has only ruled that the format for fees introduced in 2013 was unlawful, not that fees themselves are fundamentally unlawful.

Clyde & Co employment partner Nick Elwell-Sutton says that he would not be surprised to see fees reintroduced but in a more "reasonable" form.

He comments: "I don't think we have seen the last of these fees; the judgment was palpably clear that had they been more reasonable it would have probably been permitted. I think we will probably see a revamped system in which what you pay is more proportionate to the claim."

Fieldfisher head of employment, pensions and immigration Ranjit Dhindsa agrees, saying: "I think if fees were introduced that related to the value of the case, that would work. The issue here was that it was an arbitrary figure, not related to the value of the claim."

While many partners think a revised form of tribunal fees is technically viable, some argue that the current political instability and weakness of Theresa May's Conservative Party would make it difficult to achieve in the short term.

Leckey says: "My immediate reaction when the decision came out is that the government would immediately launch a new consultation into a lawful scheme. There has been no indication that they are planning to do that, in fact it looks that they are going to accept the decision.

"That could be reflective of things like the Taylor Review, that was critical of fees, but I suspect that for a minority government, dominated by Brexit, getting through any legislation would be difficult."