Merseyside is Liverpool and its surrounding boroughs, and — like Tyne and Wear — is one of the most urban counties in the country, so land for keeping a pony within it is limited and sought after. Sefton, on the coastal side, has a genuine equestrian pocket thanks to Aintree and a tradition of racing and hunting nearby, but for most family ponies buyers look just across the county line into Cheshire or Lancashire, both of which are close and well connected by motorway.
As with other dense urban counties, the practical upside is a strong network of riding schools serving a large population who want regular riding without land of their own. If you do find a pony genuinely kept within Merseyside, expect tighter grazing and higher livery costs than in the surrounding rural counties, and ask accordingly about turnout.