In a nutshell, if your contract with a wedding supplier has been impacted by the new guidelines issued by the government in light of Covid19, you should have the right to postpone or receive a refund of some sort. However, should you simply change your mind, then this does not make you eligible for a refund. Similarly, if your supplier has invested time or bought products towards your day, you must be prepared that you will not some / any of your money back. The amount will depend on the T&Cs of your booking contract and the time of your cancellation.
Not only is this a difficult time for couples, but businesses are suffering too. I always believe discussing this (not via email, but actually face to face or over the phone) is the best way forward. Make sure you have read and understood the T&Cs of the contracts you have signed AND you have an understanding of your rights as a consumer. This will allow everyone to discuss a solution to the problem in an informed manner that can be approached with kindness and compassion from both sides.