I currently have BT Fibre 1 which advertises speeds of 50Mb down / 9 Mb up. However the most I ever achieve is 33 down and 5.8 up. There's a big green BT box straight across the road. I wonder if this is normal or if there is a way to increase the speed a little (especially the upload).
The advertised speed of 50Mbps /9Mbps are what the Government has decreed that ISPs must now use in their adverts as against the old "speeds up to " that they used to use. It is in many cases totally misleading because as you know people can get well above the average and others can get well below the average.
This is explained in the small print on the BT Broadband packages web page under Important Information > The Legal Stuff
Fibre from BT
91% UK coverage. Average speeds based on speed available to at least 50% of customers at peak time (8-10pm). Your actual speed will depend on your location, phone line, home wiring, Wi-Fi connection and time of day. Check your speed at bt.com/speed. Our Fibre broadband is subject to availability, geographic location, computer specifications and a line check.
According to the checker, you would appear to be getting pretty near the top speed that your line can support.
As you can see from the checker, your observed speed of 35.24M is virtually at the highest speed your line is estimated to achieve 36M.
It is Fibre To The Premises on Demand which is sold as a business product. A bespoke fibre line will be laid to your premises at your cost which invariably costs thousands of pounds.
It means you need to take out another mortgage if you want it. It is a very expensive option aimed at business users.