I have spoken to someone from Scottish Hydro who advises that all customers* who were without power for at least 48 hours during the December storms are eligible for £75 compensation. This will not be credited to customers’ accounts but will be paid by cheque to those who submit a claim in writing. To claim, email your details to firstname.lastname@example.org. They will check that you are eligible and write to you acknowledging this (this may take a month or more as they have been inundated with claims). You will then receive your cheque within 14 days of that letter.
*I am not clear whether all residents can submit a claim (given that it is Scottish Hydro are responsible for power distribution) or whether it is only those who currently have their power supplied by Scottish Hydro.