You can see lenticulars in southern England with the right wind direction (westerly) - certainly weak wave can set up over Oxfordshire as a result of the winds hitting south Wales.
Wave is not exclusive to the immediate vicinity of big mountains.
But wave strength & height is certainly related to wind strength & mountain height - hence Scotland which gets uninterrupted airflow from across the Atlantic + the Cairngorms can equal wave to +35 000 feet in the Aboyne area. But there are other known good wave sites for gliders in Yorkshire (Sutton Bank), the Long Mynd (Shropshire) and Talgarth (South Wales) to name but a few. The general indications for the UK are steady westerly winds. The wave "seasons" for gliding tend to be October - May but it can set up at any time of the year. 500 - 800 feet/minute up or down and very strong turbulence at the bottom in the rotor are all possible.
In extreme conditions the rotor seems to be able to get down to ground level and certainly down wave has been known to cancel out what should have been good ridge lift at the Long Mynd.
But if you know where and when to look for it, it's great! (21 000 feet best so far)