I don't think that we use the term soda very much.
People used to have those soda fountain things on their "in house built-in-bars" which pumped out soda water (to go with whisky, I assume)- I never really knew why anyone would want it as it tasted fairly unpleasant. Shops still sell soda water in bottles as a mixer drink. I think it is still sold to go with whisky but I've never actually heard anyone ask for whisky and soda. It tends to be whisky (blended) and Canada Dry (for my parents' generation), malt whisky is better without any additions.
We can buy soda fountains/Sodastreams which is presumably based on the US usage as sticky concoctions are added to make not very convincing fizzy drinks. I don't think that we never had places called soda fountains (maybe because we could buy soft drinks in pubs).
There was a fashion for ice cream soda which my uncle used to buy for me at his favourite "Milk Bar".
In the North of England fizzy drinks were always (and maybe still are) called "pop". There even used to be a pop delivery van.
The word for drinks that have to be diluted was always cordial or squash in my family. I say a sign in a hotel in the US saying that soda was free but there was a charge for cordials. I was surprised, as I would have thought that cordial was cheaper. I hadn't realised that the word cordial was used to refer to alcoholic drinks.
On the subject of fizzy drinks. Lemonade is clear fizzy stuff with a vague taste of lemon - it's taste of lemon tends to be directly proportional to the price paid. The rather up-market fizzy stuff that actually looks lemon coloured and tastes of lemon, tends to be called "old fashioned lemonade" with the words "old fashioned" seen as an extra selling point. Some places sell Seven Up as lemonade but I think it has lemon and lime (but I could be wrong). Fizzy lemon and lime has the same chemical taste of lemonade but had extra lurid green dye. You can sometimes get the real still old fashioned lemonade sold in the US as lemonade, it is sometimes called lemon juice but you may need to be careful, otherwise you could end up with pure squeezed lemon.
As mentioned earlier, Coca Cola tends to be Coke, even if it is Pespi although "own brands" tend to call their stuff cola - often even more revolting than the real aircraft cleaning fluid sold as a drink.
I think that, like other foods, terms for drinks have regional/generational variations, so don't be suprised if someone from another part of the UK disagrees!
