Has anyone ever challenged the pension abatement

If you have a public sector pension and take up employment in the public sector your pension is subject to abatement. If you take up private sector work it is not abated.

This seems to be unfair. Your pension is based on your service and you have paid into it so why should you lose out through abatement? It is also a disincentive for anyone to remain the the public sector if they have done their 40 years.
Has this been challenged in the courts yet?

I agree that it seems unfair and I'm surprised that it hasn't been challenged in the courts (or perhaps it has?)

The basis for it appears to be about saving money - and the wording suggests that a public sector pension combined with a PS salary is some kind of charity that you're lucky to be in receipt of, rather than a payment for services rendered. The justification for it is not explained anywhere officially that I can find - and it's based purely on that fact that it has "always been done that way".

The principle of pension abatement has existed in the public service for many years, with its application stemming from the relevant pension scheme rules and legislation applicable to a particular public service body or sector. This meant that, historically, pension abatement generally only applied to the pensions of retired public servants who secured another public service appointment in the body/sector from which they originally retired.

Found this from a Parliamentary Question answered by Paschal Donohoe last year. Note the use of the word "valuable" in relation to your PS Pension - i.e you've won the Pensions Lotto!

The policy rationale behind abatement is to avoid a situation where individuals benefit from both a valuable public service pension and also a public service salary. In that context, pension abatement represents a suitable and measured response to legitimate public concerns and remains a key component of Public Service pension policy.

The UK public service also has pension abatement. It still applies in the same way as ours did prior to 2012, ie, to re-employment within the retiree's own sector - civil service, heath, education, etc.

I don't know the history but it is quite possible that we inherited abatement along with the rest of the UK civil service pension provisions at the foundation of the State. It has certainly been around long enough in both jurisdictions for a challenge to have been mounted if anyone was inclined to do so - or advised that it could be successfully challenged.

Our abatement provisions were generalized across the PS in 2012. It is probably not a coincidence that it was at a time when there had been fairly widespread incentivized early retirement schemes on offer.