When you are next contacted, I'm sure they will again ask you how you feel it went, if you're interested etc. At this point I would suggest you say that you feel it went well, and that you're very interested in the job, subject to the package on offer. This will open talks about salary, holidays, pension etc and it also suggests that you're not going to take whatever they offer you.
If at that point they ask you what your expectation are, (confidently) say something along the lines of 'well the job was advertised with a salary of 38k which is one of the reasons I applied for it, because that is what I would be looking for if I was going to move.' Then stop talking, and wait until they reply. The silence will be uncomfortable if they don't reply immediately, but it's important you maintain your silence. If they are experienced negotiators they may keep a silence to see if you follow up with something like 'but I would be happy to take less as I know times are hard.......' you would be amazed how many people do that! So keep your silence and let them respond.
As others have said, don't sell yourself short. Value your skills and experience and if they want you, they will have to pay what you're worth.
Very best of luck, and please keep us posted.
Read the whole thread and and the last post says what I would have said. Only thing I would add is to ask what the full remuneration package is, ie salary, bonus, overtime rate etc etc.