I'm not from the UK but the double Liberta Explorer cage looks alot like the Midwest Critter Nation double-units that I have. Looks like a great cage. You might need some metal trays to put at the full levels to keep the litter in and make cleaning easier. (Degus will chew plastic, so metal is better.) There are a couple of degu-specific forums like the Degu World Forum and Degutopia that have many experienced members from the UK that could be of further help with both cages and other issues you might encounter with your degus.
Please keep us posted – would love to hear more once you've adopted the degus.
A word of advice: Learn how to sex them or take them to a vet to sex them because alot of pet stores/rescues etc. make mistakes (degu males and females look alot alike – not like rats, gerbils, etc. that are easily distinguishable.). You can learn how to sex them from the forums as well.