I understand that the IR requires as a minimum a Class 2 medical with Class 1 hearing privileges. Now, even though your Class 1 has expired, if you look at the next hearing test dates on the Class 1 certificate, you may well find that these are still some way in the future. So, in theory you may be ok.
However, I do not know anyone who has actually used this, and many schools for “insurance” purposes may require you to revalidate the Class 1 anyway before they allow you fly IMC in their aircraft.
Better call or write to your licensing authority, and when you get the official line, post it here.
