The "Vitamin B Compound Strong" tablets you refer to are properly known as "Vitamin B Tablets Compound, Strong" in the BNF. It is an official title for this particular tablet and can be recognised by pharmacists and doctors on the basis of this title alone.
The tablets each contain 20mg of Nicotinamide (Vitamin B3), 2mg of Pyridoxine (Vitamin B6), 2mg of Riboflavin (Vitamin B2) and 5mg of Thiamine (Vitamin B1).
To be honest, they don't contain all the members of the Vitamin B group and have not changed in formulation for very many years. They were prescribable under this name when I was a lad and believe me, that was over 50 years ago!
There are lots of more modern and palatable alternatives nowadays, but they cannot be prescribed on a normal NHS prescription as they are regarded as being excessively expensive by the powers that be and the NHS will not support profiteering.
The following links will easily provide you with high strength vitamin B tablets that exceed the dose of the individual vitamins in your present tablets. These are not excessive doses as long as you follow the instructions closely. I am also assuming that you are taking these tablets on the advice of your GP for a recognised medical condition - vitamin supplementation is a debatable topic in otherwise healthy individuals. Nevertheless, you should certainly find them more palatable.
https://www.healthspan.co.uk/products/high-strength-vitamin-b-complex
https://www.naturesbest.co.uk/vitamin-b-100-complex-p641/
https://www.myvitamins.com/vitamins/vitamin-b-complex/11338697.html
You may be able to find a cheaper supplier on the web - I've only done a quick search. Don't forget to follow the instructions closely and you should be ok.
With apologies to Sqad for overeaching into his zone of expertise!!