Royal Mail with insurance up to £150 included on 24/48 hour services. Special delivery if you need more. Parcelforce for heavy and bulky.
They'll collect free of charge too, or you can just drop smaller items into a post box or parcel box (parcel boxes used to be the businesss post boxes but now everyone can use), or go to a post office. The larger post offices have scan and drop machines if you don't feel like interacting with other humans.
Just use your kitchen food scales to weigh the package and select the right weight when you order. You can then either print the label yourself (I do this and put the label inside a transparent sticky document wallet sealed and stuck to the box), or select the option for the postie to bring a label. I prefer to print myself so I can seal, weigh and take a picture myself, then all I have to do is hand it over to the postie and I'm done.
For even larger items you can check out Yodel for domestric and DHL or TNT for domestic and international.
If you send more than a few parcels per year I would recomend buying clear plastic document wallets.
Then when you print your RM postage label you just cut it with scissors or fold it so it can be slid inside the transparent wallet, then stuck on your parcel.
If you send more than a few smaller items per year then also buy some plastic self sealing bags.
When you use both of the above, it makes postage of smaller items so much easier, and looks much more professional. You can even send letters inside the plastic wallet if you want to send a letter with tracking. I just keep a bunch of them in my filing drawer, I don't even use paper envelopes for letters, small items (and returns) or returns anymore.
One thing to note, when you print out royal mail labels and cut them to size so they fit in the wallets, leave extra boundary of say an inch of plain paper on the right hand side of the label (where the arrow is in this image), which ensures the barcode doesn't slip under the "documents enclosed" decal on the plastic wallet. I keep in my desk draw A6 and A5 document wallets. I used to send out around 15 items per day like this and either have RM collect them all, or drop them all off in a post box. It's very convienent sending special delivery like this too, no need to go to a post office.
When sending special delivery I would also take a picture of the item next to the polly pocket with the label on it, then a 2nd picture of the sealed package on my kitchen scales. Although you could dump a special delivery in a post box / pracel box, I prefered the free RM colleciton. If you return stuff from Amazon then this is great because they often issue the refund just a few hours after RM make the collection before they even get the item back. If you want to you can also put other docs in the plastic wallet behind the label for the recipiant such as an RMA authorisation, or a letter you want a record of delivery such as serving legal docs.
Once you send/return items like this you wont go back to whatever you do right now, it's so quick and easy, and looks professional. You can use the same process with other couriers too, that's when I often use the A5 instead of A6 document wallet. They are self adhesive so you just peal the back and slap them on the bag or the box, all self-sealed and no messing around with tape.
