I would recommend to the house 'Parcel2Go'.
I had a 14kg parcel to send within the UK and with these guys you can choose the option best suiting your needs.
You can have the parcel collected from your house or take it to a despatch point. In my case I used the Parcelforce option as I got a choice of Post Offices to take it to. You can choose insurance value although in my case it was moot as the contents were pretty much irreplaceable. Having booked everything and printed off the address label I took my parcel to the P.O. Thursday 16th and it was delivered today 20th.
The whole transaction was easy and painless.

www.parcel2go.com

As far as I can see, it's little more than (yet another) price-comparison site, this time with a specialism for Parcel services?

I find these sites useful to find suppliers I'd not thought of, but often once you have selected a supplier, in many cases it's cheaper to go to the supplier's own website direct and get a new quote rather than via the link from the comparison site...

I used parcel supermarket - the only drawback (for me) was having to print off the labels. I didn't mind taking my (very heavy - over 25kg) load down to the post office and it saved me £££loads!
https://www.postagesupermarket.com/parcel-delivery/uk/

Just never EVER use Evri (Hermes as was) unless you never want to see your parcel ever again except maybe on ebay or at a car boot sale...

With the value of contents in the parcels I regularly send, for me it has to be Royal Mail every time. I often use their 'Precision' service special delivery guaranteed by 1pm next day.

For a 10kg medium parcel with the value of contents covered up to £1000 it cost's only £15.45, for contents of £2.500 £17.45.

Also worth mentioning their 2nd class 'signed for' small parcel service which today only costs £3.95. I've been using that service for many rears now and never had any problems.

I've recently tried Yodel 'store-to-door' service, and have been pleased with the service. I fit in dropping off my parcels when going in to town to do the weekly shop. I've also used the Royal Mail collection service, it is a bit more expensive, but does save having to take parcel(s) to a drop off point.
Cheers

We're sitting now in the United kingdom, right now I'm running 2 local business brands in the UK. And I've been using couple of courier companies, Having a very good experience of shipping on time and the safety of my stock. I usually get my shipment within the same day of the delivery order. The 1st one is national couriers direct and the 2nd one is parcel2go.

Parcel2Go aren't a courier, just a price comparison website. Useful, but you can only really recommend them in the context of the experience (as NN did in the OP), rather than anything delivery related.

Personally I use Royal Mail whenever possible. I find them consistently reliable with good pricing as long as it's within their 'small parcel' dimensions, outside of that it gets expensive! 

I'm sending pretty much all the small items these days via Royal mail 'Tracked 48'. Great value for money and covers items up to £150.

Yep, that's my go to service as well. Does what it says on the tin.