In England for example sometimes are cited the coronavirus regulations rather than say the Highway and safety Act. What are the differences between these two types of instruments?
An Act is what's called Primary Legislation, where as Regulations are Secondary Legislation.
An Act of Parliament is a law that both Houses of Parliament have agreed to and which has received Royal Assent. These Acts may include provisions for secondary legislation which is law created by ministers (or other bodies) under powers given to them by the Act.
The UK's Legislation website says this:
'Primary legislation' is the term used to describe the main laws passed by the legislative bodies of the UK e.g. Acts of the UK Parliament, Scottish Parliament, Welsh Parliament and Northern Ireland Assembly. It also includes Acts passed by historical parliaments, other primary legislation for Northern Ireland and Church of England Measures (legislation for the established church in England passed by the General Synod of the Church of England).
These types of legislation are sometimes referred to as 'statutes' and the term 'the statute book' refers to the whole of the statute law currently in force.
'Secondary legislation' (also called 'subordinate legislation') is delegated legislation made by a person or body under authority contained in primary legislation. Typically, powers to make secondary legislation may be conferred on ministers, on the Crown, or on public bodies. For example, the Office of Communications (OFCOM) is given such powers by the Communications Act 2003.
The main types of secondary legislation are Statutory Instruments, Statutory Rules and Orders, Church Instruments.
There are three main types of UK Statutory Instrument: 'Orders', 'Regulations', 'Rules'. However, there is no limit imposed on the descriptions that may be given to Statutory Instruments. Other examples include 'Scheme', 'Direction' and 'Declaration'. Different types of instruments serve different functions, but they all have the same legislative force. Prior to 1948, when the Statutory Instruments Act 1946 came into force, the equivalent instruments were known as 'Statutory Rules and Orders'.
For example, Part 2A of the Public Health (Control of Disease) Act 1984 allows for the making of secondary legislation regulations such as (the now revoked) The Health Protection (Coronavirus, Restrictions) (Self-Isolation) (England) Regulations 2020
Secondary Legislation is still subject to Parliamentary scrutiny as it must be approved (the affirmative process) or not rejected (the negative process - and the one applicable to the majority of SI) by Parliament.