The current salary is a difficult question, and it is true, they will use this to base their offer to you.
I wouldn't even say what you're looking for. You could be looking for £50k for example, and get it, and then find out everyone else in the team is getting £60k.
I'd put 000 or 111 on the salary questionnaire.
During interviews, you do have to play "hard ball". I've always said along the lines of "I don't want to focus on my current salary, as it's a different type of job with different targets and a different way of working, plus I'm looking to leave (ha. ha.) I'd like to focus on this role and as you know more about this role, what the job entails and my experience from my CV, perhaps you can suggest to me a range which would be fair for this position?" And leave it as that.
I'd continue to stay on the fact that your current salary is irrelevant, because in which case, you might as well ask what the person who currently does this role, is on...If they don't budge, then they aren't the company to work for. Every company has a budget.
Some companies say they don't like to share a budget because applicants automatically put themselves at the higher end of the scale. Which to me doesn't hold much water, because the company should be able to justify why, when they put someone on the scale.
Salary is the one thing you have the upper hand about as someone who is applying for a role. A company can base their salary not only on the job, but also on the success on the company, potential investment and expansion in that department, how desperate they are to fill the role, how long the role has been open for, how much out of hours work you're expected to put in...which you may not necessarily know about. But they do. Let them say a number first.