Lawyers draw a strict line between what’s arguable and what isn’t. An arguable point is one that a lawyer can properly put to a judge. An unarguable point is one that it would be professional misconduct to present. For example, a lawyer can’t say that the qualifying period for unfair dismissal is 6 months; the law is clear that it isn’t; to argue that would be a short-lived attempt to mislead the tribunal.
But that distinction is a bad guide to what points you should run. Lots of arguable points are still pretty bad. It’s perfectly arguable to say ‘Madam, it was outside the range of reasonable responses for my client to be dismissed for stealing £10,000 from her employer.’ But no sane tribunal is likely to agree with you.
So if your reply to the question ‘Why do you want to present this argument?’ is ‘Because I can — it’s arguable’ you’ve gone wrong somewhere.
Rather than assembling all the arguable points you could possibly run, focus on finding your best points: the ones that are most likely to persuade the tribunal. Stick to those, and don’t run arguable but weak points just for the sake of it.
Sometimes this will still mean running weak arguments. If your case is weak, but your client is determined to roll the dice, a weak argument may be the best you have. Or, if the potential upside is sufficient, it may be worth taking a low-percentage bet. For example, since discrimination awards are uncapped it might be worth arguing a weak discrimination claim, in addition to a strong unfair dismissal claim, in the hope of obtaining much higher compensation. But, if your likely award is well below the unfair dismissal cap, the calculation changes, and it will almost certainly be better to concentrate on your best claim.