3% rent increase reasonable?

We currently let 3 properties, all of the tenants have been our tenants since we purchased them in early 2017. We haven’t increased the rent since, however we would like to do so this year.

All of the tenants are on a periodic tenancy agreement and the AST has provision for a rent increase –
Section 9) If the Tenant remains as the lawful Tenant of the property for more than 12 months the rent will increase once each year. The first increase being the first rent due date more than 365 days after the commencement date.

We are considering increasing by 3%, would this be reasonable?

I’d appreciate any advise on the process to do this. Research on this forum has pointed to issuing a Form 4, however, this refers to property rental in England and we are in Northern Ireland.

If we were to write to them advising of our intentions and then issue a new AST would this be suitable?
Could we amend the rent increase clause to state that it will increase by 3% annually going forward.

Are there any other implications to consider?

Any advise would be appreciated.

Ann