If you are going to ask a group of people to sign a register, you need to know who you are asking. My professional body, the CIPR, has launched a 'debate the definition' page on its website to encourage people to comment and discuss how to get to the right definition.
Clearly, the act of lobbying is about engaging with policymakers. That engagement might be to influence public policy, but for much of the time it focuses on ensuring that you understand the Government's intention and provide information that helps politicians and civil servants make better policy.
There are some who provide high-level advice to their clients or employers on the way politicians view an issue. Those advisers may not be directly influencing policy but may be helping others to do so.
The CIPR believes they too should be on the register. There is logic to this but the problem is where do you draw the line? Is general advice on how to talk to a politician influencing government policy? Then there are those who are not employed as a lobbyist but might be as effective in the role as communicators: the CEO of a FTSE 100 or the policy officer of a trade body, for example.
Making sure you have a workable definition is not going to be easy.
In today's world, public relations is multi-disciplinary. Many agencies offer public affairs alongside other comms services. Even when functions are separated it is imperative that they work together.
A public affairs professional would not be doing their job if they didn't understand the impact a media campaign was going to have on an issue they were dealing with. There is some way to go before we have a definition that adequately encapsulates what a modern-day lobbyist does.