It doesn’t matter how careful you are, an employee can turn out to be a disaster. For a new hire, they might look good on paper and perform well at interview, but as soon as they take up the role, they may fall short of the mark.
If, during the first four weeks of employment, they are not up to scratch, then you can let them go with no notice. So no trial period is needed. From then on, you continue to train and assess.
The biggest mistake our members make is to say "for a three-month trial period". When three months is up, you could be short-staffed, on holiday or have a busy Christmas period, for example, and you forget to interview them. Is it OK to do it a week later when things have quietened down or you have just remembered? No. The courts have made it very clear that if you miss this by just one day, employment is automatically confirmed. Redundancy payments are not an issue until after two years’ employment.
Have a chat now and then. Tell them you are pleased if it is going well. Or, if there is a problem, but it’s not too serious, tell them you are reasonably happy, but would like to bring to their attention to this or that issue. Later, if they are not suitable, you can remind them of your chat and say that, regrettably, you have to let them go.