Thank you to everyone who has given advice and opinions on this.
We visited today, checked the electrical work had been completed and took away the rubbish left by the previous tenants in the outside storage cupboard.
I am not going to change agents. We have found them to be perfectly satisfactory and diplomatic with previous tenants. I will not be hunting around for others just because one employee failed to pass on a message. Indeed she says she had emailed them informing them of our intention to visit, but received no response to say it would or would not be OK, until yesterday when we pressed for an answer and contact was made.
They seem sensible people, the woman and baby have not moved in yet, the husband is a surgeon so probably busy, hence not returning agent's emails or being easy to catch on the phone.
The agent has told them that they are responsible for storing the bed, the cellar is an option but it must be returned in its current condition, and they do not have carte blanche to remove any other items. The deposit would cover a replacement bed, though I do not anticipate it coming to that.
To the person who suggested we were being petty not to want to transport a bed which was clearly part of the let, and which was not queried at the outset, 90 miles away, store it and return it later, I would say ODFOD.
Thanks again, the situation seems resolved. If any other problems arise, I will come back for helpful advice from most of you, and give others an opportunity to deliver a good kicking.