If you have worked for your employer for less than two years you generally have little protection against being dismissed unless it is for an automatically unfair reason such as whistleblowing or discrimination. So if the employer decides to dismiss you for failing to meet targets, you are unlikely to be able to take action against them.
If you have more than two years’ continuous service, your employer can take disciplinary action against you but it needs to be fair. You may be able to claim unfair dismissal if the targets are unreasonable, if you are not given the training and tools you need, or if the employer does not follow a fair disciplinary procedure. If all these steps have been taken, you can be dismissed for failing to meet your targets.