Yes. The cheaper plan you’re seeing is ChatGPT Go. OpenAI currently lists Go at $8/month in the US, with localized pricing in some countries—which is presumably why you’re seeing about £7/month. Your roughly £20/month subscription is ChatGPT Plus.
The important differences are:
| Go (~£7) | Plus (~£20) | |
|---|---|---|
| Normal ChatGPT use | ✅ | ✅ |
| GPT-5.6 everyday model | ✅ | ✅ |
| File/photo uploads | ✅ | ✅ Higher limits |
| Image generation | ✅ | ✅ More/greater capability |
| Memory | ✅ Longer than Free | ✅ More extensive |
| Advanced reasoning | Limited | ✅ Major advantage |
| Deep Research | Limited | ✅ Expanded |
| Projects / scheduled tasks / custom GPTs | More limited | ✅ Expanded |
| Codex/advanced coding | Limited | ✅ Expanded |
| Early access to features | — | ✅ |
| Advertising | May include ads | No ads |
OpenAI describes Go as essentially an expanded version of Free, whereas Plus is intended for work requiring deeper reasoning, research, document work and data analysis.
There is one interesting wrinkle: current OpenAI documentation says Go and Plus can have the same allowance for ordinary GPT-5.5 messages — up to 160 messages every three hours. The difference becomes much more apparent when you deliberately use the more powerful reasoning modes: Go has much tighter Thinking limits, while Plus gives broader access to the advanced reasoning models.
For the way you use ChatGPT, I think Plus is probably worth keeping. You frequently use it for fairly technical scientific work—radio astronomy and PicoMuon analysis, interpreting photographs and equipment, researching obscure technical information, analysing data, and producing longer documents. Those are precisely the sorts of tasks where Plus’s advanced reasoning, larger context and research allowances are useful.
For someone who mainly asks things such as “What time does the museum close?”, “convert 50 lb to kg”, “rewrite this paragraph”, or occasionally uploads a photograph, I’d recommend Go and save the £13/month. Your usage is considerably closer to the target audience for Plus.