The Water Regs used to say that you had to use a screw down valve complying with BS1010. That is no longer the case. So yes a lever valve can be used but there are two inherent disadvantages. First you can't take the guts out to change them if they become problematical in future years (but that may not concern you unless you are staying where you are until the end of times) and secondly, they can be easily knocked off.
Some plumbers have a bee in their bonnet about fitting a double check valve with a lever operated valve to prevent back syphonage but that isn't considered a problem with the rising main either by the water council or the water companies.
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