For a start the issue of bonding etc. are irrelevant in this case.
The company have no right to withold this information and are actually breaking DfT rules if they won't confirm your dates of employment.
Many companies try this on for whatever perverted pleasure they get out of it, but they are just getting themselves in trouble for being intransigent idiots.
Contact BALPA about this, they know all about it, having dealt with a friend who had a similar problem. Strangely enough that was with Emerald aswell!
In the end though, his new company got so annoyed they wrote to the airport who were issuing the ID and just told them that they thought Emerald were going bust and so probably weren't capable of providing a reference. This seemed to satisfy them.
Ring them up and ask point blank why they haven't filled in a very simple request, it's not exactly rocket science so why they should be such muppets I don't know?