If I buy an isofix carseat can I use it without isofix?

[SlightlyMadShrek]

Looking at new carseats for DD3 (like everyone else).

I know isofix are suppost to be safer, but the middle seat in my car does not have isofix points.

I will use the seat on the outside most often but for logitistical reasons occasionally move it to the middle. Do they have the option of using with a standard seatbelt?

I have a Britax Isofix Duo Plus (9mths-4yrs) and that can either be isofixed or belted in.

ty, that is the sort of thing I am looking at.