Leasehold management company right to interfere with leasehold rights

I have a 135 year lease of a flat and a garage. The plan shows an area of six parking spaces for general use amongst 12 tenants which in 1978 I guess was not a problem. The lease is specifically silent on parking rights save for the plan. The management company (which has directors who have no idea of company or any law) have just instructed solicitors and had a special regulation drawn up stating commercial vehicles cannot park on the premises. I was not informed of any meeting where this was going to be discussed and have just let to a tenant who has a semi commercial vehicle. Notwithstanding the directors may not have complied with company law, do they have the power to interfere with a right to park in one of the six designated spaces provided by the lease? And, do they have a right to instruct solicitors to draw up a regualation if they dont have that right?