Yes. Have a look on eBay, there are plenty of people offering postal services much less than Post Office/Parcel Post charge. Basically they have a corporate account, so the rate they pay is probably less than half the public rate. They then sell on individual deliveries undercutting Parcel Force.
I used this when I had to return some garden tools to be replaced. Parcel Force would have been £11, I paid £5.99 to the supplier. Parcel Force came to my door to collect the parcel the next day, and it was with the supplier the day after that.
Only downside as you have to be in when they come and collect.