Apparantly a German passport gives you the most countries you can enter without a visa, 176 out of 218. The BBC news quiz says that the UK is equal fourth but doesn't specify the number. So what are the countries that a German can enter visa free that somebody from the UK can't?
So what are the countries that a German can enter visa free that somebody from the UK can't?
Visa free or VOA (when UK passport needs a proper visa)are Marshall Islands, Mongolia, Palau, Samoa, Solomon Islands, Timor Leste, Turkey, Tuvalu, Tonga and UAE.

Well I am not sure about UAE, the embassy states "Citizens of the UK (with right of abode in the UK) will be granted a free of charge visit visa on arrival in the UAE. No application in advance of travel is necessary. Please note that your passport will be stamped for 30 days upon arrival." So perhaps Turkey is the only significant difference.
Visa free or VOA (when UK passport needs a proper visa)are Marshall Islands, Mongolia, Palau, Samoa, Solomon Islands, Timor Leste, Turkey, Tuvalu, Tonga and UAE.
What has the UK done to upset these countries?

Not sure where that list came from but it is bogus, Palau, Samoa, Tuvalu and Tonga also do not require visas.
I think there are several different and competing lists.
They don't even agree on what constitutes a "country" ,or how many countries there are in the world.