The efficiency of your boiler depends on several factors, let's forget about how well-insulated your house is for a short while and concentrate on the boiler output.
Output or Flow temperature settings.
Firstly, a boiler is like a car engine; the harder it's pushed, the more fuel it uses for a specific output. If your boiler runs flat out for 4 hours a day, it might save fuel by running it at a lower temperature for 6 hours a day. Every property will be different with this, but you should try reducing the boiler output temperature to between 50-60 degrees Celsius, and if it's not giving the heat you require, try adjusting the temperature up each day a few degrees until the ideal temperature is reached.
Different Types of Boiler Controls.
After working out the most efficient boiler flow temperature, you should look at the boiler controls, some manufacturer controls vary the boiler output to how close the temperature is to the room thermostat set temperature, if it's just under the required temperature the boiler will only work at the part fan (throttle) and the gas usage will be reduced for this period. Whereas non-manufacturer controls generally power the boiler by an on/off signal giving a non-modulated output.
Old vs Modern Boilers.
All new modern boilers are room sealed. If you still have an older (open-flued) type boiler and your property has air supply vents through the walls, the first piece of advice is to look at a modern replacement. You will soon begin to save money monthly. Your boiler should have been sized correctly for the property, which will be the case for most - but over time, many of the UK's houses have had extensions and alterations to maximize the space available, so maybe it's worth looking at the boiler output again and checking you have a suitably sized boiler for the property.
Boiler Servicing, safety, and efficiency.
Frequent servicing of your boiler will help to maintain safe operation. It's generally known in the industry that a yearly service can help to maintain the efficiency of your boiler and save money on costly repairs or premature replacement. Most manufacturers supply a good length of warranty on replacement boilers, and for this to be honoured, evidence of yearly servicing will be required.
Radiators and Underfloor heating - Heat emitters.
Radiators are a big topic, but generally, with modern boilers, the higher output the radiator has, the less heat is required to flow through it to heat the room, and this saves you money as the boiler does not have to work as hard. If you are considering replacing radiators in any part of your property, have a heat loss calculation. It's fairly simple to do - there's also plenty of help online and some free calculators that might help the keen DIY'ers.
For existing radiators or UFH (under-floor heating systems), you should ensure they are working well - no cold spots or air in the system. If you do have cold spots, there are ways for the professionals to help, mainly with heating system power flushing, which uses chemicals and higher flow equipment to clean out the heat emitters one by one. This process generally costs between £200-£600 depending on the size of the property and the level of corrosion/blockages in the system.
Another good idea is to reduce the temperature on the radiator's thermostatic valves in rooms that are not being used or do not require as much heat.
Insulating your property.
And finally, generally, the highest cost improvement is how well your house is insulated. From closing doors and windows during the coldest months to the insulation in your walls, floors, and ceilings. Simply put, the less heat you allow out, the less heat your boiler will need to supply.
It's worth ensuring you have no air leaks around doors, windows, or anywhere else. In most Shropshire properties, the most cost-effective insulation is in your loft space. Easy to check and relatively cheap to add more if required - most DIY shops sell it on the roll. Modern windows and doors will be a big benefit but can become costly.
A quick Google search will provide plenty of information on methods of insulating walls effectively. Most houses have cavity wall insulation, but if not, then it's worth investigating as it's generally quick and relatively cheap, depending on the method. If you're having major renovation carried out then it's possible to add insulation internally or externally to walls and under your floors but again this will be a costly improvement and you may need approval from your local council or building authority before commencing this work. It's worth discussing with your builder before starting the project.