Although the answer to this question for many people will be an unequivocal 'Yes', the question carries a range of nuances that will be important to anyone asking it.
When carrying a common object intended for self defence, in many legal jurisdictions, the UK included, the legality of use is defined by the intended and relevant application of the object as stated to the authorities, if challenged or questioned.
Carrying an everyday item such as a tactical pen, a tactical torch or a spray can is legally acceptable - AS LONG AS the declared purpose and potential usage of the item appears reasonable and relevant.
For example, giving a reason that a tactical pen is carried by you to be used to defend yourself if attacked makes the item an offensive weapon in law and carrying it actually becomes illegal.
However, explaining that you have it on you because you anticipate to use it practically, such as together with a notebook or that you actually use it regularly in your daily work, makes it permissible if you rely on it as a reasonable force tool in a violent confrontation. You simply carried it as it's your every day habit to do so.
A tactical torch in your car or on your walk on a dark night, such as with your dog, is purposefully useful if you or someone else has a vehicle breakdown or to clear the business from your pet and can be explained, post-incident, as a reasonable item to have at hand.
The similar principle applies to common objects as self defence tools you plan to use in any intruder scenarios, such as within your home.
If you hit an intruder with the heavy metal lamp on your night table, it might be ok (if genuine fear for your safety was present and reasonable force was applied) but if your explanation to the police on their arrival is that the lamp was intentionally and strategically placed there to be used to strike potential intruders with, you’re now in potential legal trouble.
The same applies to a base ball bat under your bed or a knife on top of your drawer. They must have a purpose of being there, such as being stored there with the rest of your baseball equipment or the knife is left on a plate next to the orange you were eating to slice it up with.
The point of this post is this: As a self defence practitioner, take advantage of common objects as self defence tools but invest thought in how you make these relevant to your daily activities and be clear on how you would appropriately and reasonably position their existence to the authorities, if questioned.
You should have this explanation clear. Even better, make sure that others, such as your family or friends are aware of their ‘every day’ use, so they can later testify on your behalf to validate your ‘genuine’ reason for carrying or keeping them.
Carry a tactical pen? Make it your work pen, freely seen by all. Carry a tactical torch? It’s on your belt for walking the dog at night, making sure you are a friendly neighbourhood ‘poo scooper’. Whatever you carry, have the back story ready.
Finally, of course, make sure you receive training on how to use your self defence tools of choice, making you ready and prepared if you ever had to use them.