The simple answer is yes. However, whether an employee can be dismissed for poor performance prior to the end of their probation period will largely depend on what is contained in the contract of employment and any associated documents, for example:

If an employer does not stipulate a probation period they would be expected to follow any applicable disciplinary/dismissal procedure prior to the dismissal, and must give the required period of contractual or statutory notice (whichever is greater).
If an employer does stipulate a probation period they would be expected to follow their own probation process, and any applicable disciplinary/dismissal procedure prior to the dismissal, and must give the required period of contractual or statutory notice (whichever is greater).

Ultimately, an employer does not need to wait until the end of the probation period before dismissing an unsatisfactory employee – the employee can be dismissed during the probation period. If the employee performs below the expected standards during the probation period, the employer can take the necessary steps to dismiss them without waiting for the probation period to come to an end. The employer should ensure that it follows any applicable contractual disciplinary/dismissal procedure prior to the dismissal and must give the required period of contractual or statutory notice, whichever is the greater.

You can find out more about probation periods here.