My free advice for a fellow expatriate - do NOT use online forms to inform them about address changes. You might try it out but be prepared to follow up the situation yourself. In case of Edinburgh council they provide online form for address change but it is not taken into account. Therefore I ended up sorting out the situation by emails and phone calls. In case of Scottish Hydro I used their online form with a similar result. In this case email enquiries were not replied to, so several phone calls were required.

The preferred way is to send an email or a letter informing the organization about the change, wait a week or two and then call them to check that it is actually received and processed correctly.

Never assume that things would work on the first attempt in this country...