QUOTE:
Highway Code Rule 144
You
MUST NOT
Drive dangerously
Drive without due care and attention
Drive without reasonable consideration for other road users.
Driving requires focus and attention at all times. Remember, you may be driving dangerously or travelling too fast even if you don’t mean to.
Law RTA 1988 sects 2 & 3 as amended by RTA 1991
Rule 146
Adapt your driving to the appropriate type and condition of road you are on. In particular
Do not treat speed limits as a target. It is often not appropriate or safe to drive at the maximum speed limit.
Take the road and traffic conditions into account. Be prepared for unexpected or difficult situations, for example, the road being blocked beyond a blind bend. Be prepared to adjust your speed as a precaution.
Where there are junctions, be prepared for road users emerging.
in sideroads and country lanes look out for unmarked junctions where nobody has priority
Be prepared to stop at traffic control systems, road works, pedestrian crossings or traffic lights as necessary.
Try to anticipate what pedestrians and cyclists might do. If pedestrians, particularly children, are looking the other way, they may step out into the road without seeing you.
END QUOTE.
As to 'driving too slowly', if you are driving as you would in your driving test, within the speed limit at a speed appropriate to the road conditions, at the correct thinking/stopping distance between yourself and the vehicle in front, rather too many drivers will think you are driving too slowly. In a 30 - they want to do 40, in a 40, they want to do 50, come what may.
That said, if people drive too slow for the conditions, they irritate other drivers who then take chances to overtake. On motorways and dual carriageways with a 70 limit, if conditions permit, it seems to me that anything below 50 in the inside lane can pose a hazard and impede other traffic.
Minimum Speed Limits and Driving Too Slow
On motorways, rather too many people stick in the middle lane mile after mile which risks a fine and points, and too many HGVs drive far too close to each other. Ironically, they often have a notice on the back door saying 'If you can't see my mirrors - I can't see you', yet all they can see is the back door of the HGV in front of them.
The Institute of Advanced Driving 'IPSGA' system of driving & riding has much to commend it. It’s based on the police system of vehicle control and forms the foundation of the IAM Advanced courses. Advanced Driving and Riding is all about the continuous application of IPSGA whenever you are out on the road, which helps you to adopt a systematic approach to any hazard that may arise.
‘IPSGA’:
Information.
Position.
Speed.
Gear.
Acceleration.
What is IPSGA | IAM RoadSmart | Tips for Safe Driving
Hope that's of interest.