I had a very bad experience with Parcel2go. I had 2 parcels damaged, filled in a lengthy claim form, and got no response. I phoned "Customer services" only to be told that the claims dept won't take phone calls I had to email them. I emailed, got no reply so phoned customer services again, got the same reply. After 3-4 circuits as detailed I gave up. Never did get the claim sorted.
Since that happened I use
www.interparcel.com Same idea, the difference being that on the very rare occasion something goes wrong their customer services do what it says on the tin........ Help you.
Royal Mail also collect. You have to pay online and collection is just 30p extra. If you are returning an item from an online purchase and you've been sent a postage label you can book a collection only using the tracking number on the label. That's usually free.