It sounds like you don't really have a choice in this matter, as you can't attend the interview in Germany and the one at home. If you were to take the leap and fly out there at the cost of missing the interview at home and taking time out from your current job and then be unsuccessful you'd be out of pocket as well as disappointed.
Really then, you have nothing to lose by asking, so you should go about it with a positive mindset.
Interviewing by Skype or similar service will be preferable to telephone, if the employer has the technology to do so. They will want to see you so they know that they are talking to the right person. Some positive things about asking for this are:
- It demonstrates initiative.
- It is an innovative use of technology, and they might be looking for that in the role.
- You will be able to dress up in your best suit and make a visual impression as you would in a real interview.
Thank you for the invitation to interview. Because I am living and currently working in the UK can we arrange an interview by video conferencing?
See what they say. I think there is a good chance they have done his before, it really is not all that uncommon these days.
Even though Skype is widely used and fairly well respected, there are more professional enterprise solutions out there, so it might be an idea to ask them which they normally use, and suggest Skype if they don't have a preferred solution.
Let them advise you, but if they are unsure about it or haven't done it before, take the lead and suggest:
We could set up a meeting on Skype, or any other conferencing system that your ICT team advise? Or alternatively we could conduct the interview over the telephone?
This covers all options open to you, including the telephone as a fall-back option if they agree to it.
If they don't go for it then as I already said, you would be taking a risk flying out there at the cost of the other interview, unless of course you want this job so much more that you believe it is worth the effort/risk.