DC only had one uni of their five ask them to interview with a physical portfolio (Falmouth). Everywhere else made offers on the basis of an online portfolio - all with different requirements in terms of what they wanted, how many images, how it was to be sent / uploaded and whether they wanted text / explanations or not. It was an incredibly fiddly task.
Best tips:
Have a basic portfolio ready before the UCAS form is submitted as portfolio submission deadlines can be a matter of only a week or two post request.
Unless you're applying for Oxbridge, don't submit before January to give yourself maximum opportunity to include some very recent work (especially if doing an art foundation). You will need the Xmas holidays to work on the portfolios in any case.
Set out your basic portfolio as a series of PowerPoint slides which can be edited / reordered / chopped / text added as per the individual requirements of each university.
Read the requirements carefully so you submit exactly what they have asked for. When they say they want to see experimentation and processes as well as finished page, they do mean it. Usually a mixture of sketchbook pages and finished pieces are requested.
Diarise submission deadlines and perfect each portfolio in a sensible order.
(DC ended up with offers from everywhere they applied)