Change car tyre size

[Beetlejuic3bj]

Hello and apologies for asking this question. I have done a search and i know it has been asked before but i couldnt fully understand exactly if i am allowed to or not.

I currently have a Hyundai i20 2015 which has 195/55/R16 91H tyres on which "because reasons" are significantly more expensive than other sizes.
Can i put 205/55/R16 94V tyres on the car?
I bought 4 x 205's from National (Halfords) but when the guy came to fit them, he looked at the car and refused to put them on as i had a different size tyres (195) on the car, he said it was illegal.
I have done some research online and cannot see anywhere that says it is illegal.
I know about the difference in Speedo but i've used a website which i saw in another post and the difference would be something like 1.77% which is not a lot.
Any information would be appreciated.

Thanks