Letter of offer from mortgage provider

Hi, I have an offer on a house and I’m currently waiting on the ‘letter of offer’ from ICS. I have been waiting 6 weeks and need to move into the house ASAP. My wife is pregnant and is due at the end of April. We are FTBs and both work in the public sector,
Is anybody else waiting a long time to receive the ‘letter of offer’ from their mortgage provider. ICS told me it would be 2 to 3 weeks. Is anybody else having problems.

Thanks for your help

Perfectly normal (well, in these times).