It will improve your business very much if you have:
1. Bigger Car Parking facility. Customers will then buy more groceries and then there will be better business for you!
2. Home Delivery services like other supermarkets. For long distance deliveries (more than about 4 miles), you can charge a delivery fee of about £3.00 or so. You can also include a minimum shopping of £100.00 for home deliveries.
Apart from these, I have no other suggestions. You are doing a very good service already. We are very satisfied.