IIRC the time limit for ET claims of this nature is 3 months from the date at which the money would normally have been paid. Why have we therefore not heard of ET's in the Heathrow area being paralysed by such a volume of claims ? We can only assume that potential claimants are out of time. Claims of this type made in time are usually conducted in a "quick" procedure held before a Chairman, and not a full panel, to get them out of the way expeditiously. We must assume also therefore that if claims have been made in time, that they would have been expedited using the simpler hearing.
The time limit for a Civil Breach of Contract claim (ie to a County court, not an Employment Tribunal) is more extended. However, unlike an ET where there is an automatic presumption in favour of the claimant until an employer proves otherwise (the employer is called a Respondent, not a defandant), civil court procedures require the claimant to prove that a contract has been materially breached, and the defendant to attack against the claimants evidence. This means that the defendant in this case can legitimately say "prove you were ill", whereas as a Respondent at an ET can only provide evidence to demonstrate that the claimant may not have been ill.