Is it legal for an employer to reduce the pay of her employee from above minimum wage to minimum when implementing the new minimum wage 2020

First query

In the year 2019, I was paid £8.55/hour but when the April 2020 minimum wage was implemented, I was just given the £8.72/ hour which is just the minimum wage for this year without prior notice that this year, I would be reduced to a minimum wage earner. Is it correct to interpret it that there was pay cut since I was already entitled to a pay higher than the minimum wage several years ago. This year my employer implemented the minimum wage and increase of pay despite the pandemic. Please enlighten me in this regard.

Second query

Should an employer provide an objective guidelines for salary increase or is it just within the absolute discretion of the employer even if the employee has had acquired related added qualification. Can an employer absolutely disregard added qualification for an implementation of salary increase. Will this not amount to unfair practice when others who have the same qualification (NVQ, QCF) are receiving higher increases simply as an exercise of discretion without any objective and clear written guidelines?

I am raising the first query for and on behalf of my husband and the second query applies to me.

Thank you very much.