Dismissal for taking part in properly organised strike action, excepting in long term action, is automatically unfair:
https://www.citizensadvice.org.uk/wo...issal-is-fair/
The employer though does not commit a criminal offence even if they knowingly dismiss for reasons that are automatically unfair. The dismissed employee's remedy is to make a claim to an Employment Tribunal. As has already been pointed out there is a maximum award the tribunal can make. Going to a Tribunal isn't an easy option, the form filling and procedure can be onerous, more so if the respondent employer and their lawyers choose to make it so. There's also a strict time limit. Then there's a day in court with a Judge etc to be faced. Furthermore there were, until the Supreme Court ruled them unlawful, extensive and costly fees.
The effect is that the 'go to law' option is anything but a level playing field. The claimant is prone to being picked off with a settlement (usually with confidentiality clauses) to save the Employer the embarrassment of an actual judgement.
As has been pointed out already even if the Tribunal makes a full award that''s chicken feed for the employer and probably a 'price worth paying' to pick of the ring leaders of even lawful industrial action.
It's arguable that Trade Unionism and Industrial Action in UK got out of hand in sixties/seventies. Legislation passed in the Thatcher era swung the balance too far the other way and succeeding governments, even those that were ostensibly Labour, had no appetite for a return to fairness and equality of arms.