What happens if I stay more than 24 months in the same contract?

Additionally, moving to another Umbrella company after 24 months does not change this situation, as the rule applies to your 'place of work' not the Umbrella Company you use.

The 24 month rule states that the cost of travel from your home (being your permanent place of residence) to your contract client address (your temporary workplace) is only allowable as a tax deductible expense for as long as you believe your contract will not exceed 24 months.  At the point where you know your contract will be longer than 24 months (for example if your contract is extended at 20 months for a further 6 months) then you should not claim travel expenses from the 20 month point, as your deemed a permanent employee in the eyes of the revenue.