Yes, you can install CCTV in your UK home, but there are regulations you must comply with, including the Data Protection Act 2018 and the General Data Protection Regulation. You should also ensure that your system is not invading the privacy of others and does not violate any other laws or regulations.
A basic bell-only, wireless sensor installation for a home alarm system can be done for as little as £500–£525. This is the most prevalent sort of setup in the UK, and it provides excellent security for the money.
Installing an alarm system that is approved by your insurer will increase your home's security, but there is no assurance that this will result in a lower premium.
All commercial buildings in the United Kingdom are required by law to have what is called "an acceptable fire detection system." This means that a fire can be found and the people within can be alerted quickly. This is not to say that every commercial building needs a fire alarm.