Will butane be fine for an outdoor bbq rather than propane/patio gas? is the difference negligable?

Propane has a higher butane content in Europe, and I ume the UK, than what we have here in North America. So any answers you consider accurate must consider this fact. But I will say that butane is an oily gas with a lower pressure than propane. I would say the air fuel mixture will require definite adjustment. Using a different fuel than what the appliance is certified for may cause a void of warranty and liability if anything were to happen that injured anyone or caused property damage. I suggest you contact the appliance manufacturer to get the answer for this question.