The argument that using Huawei to build a 5G network gives them an immediate backdoor into the UK's communications may be valid, but it's not hugely persuasive on its own. This is because I'm sure GCHQ, MoD and friends are capable of running their own highly secure networks separate from the public internet.
What I do find convincing is that highly cost-driven outsourcing of comms infrastructure development and more crucially, ongoing operation to a vendor based in a non-allied state is a dangerous long-term choice. It has the potential to hollow out the talent pool in domestic communications providers to a point where they are merely consumers of 'access network as a service', handing all the power to the vendor. I believe that the survival and prosperity of domestic comms engineering talent and vendors in allied countries such as Nokia, Cisco etc. are valid national security concerns.
To answer the original question, at a consumer or small business level I wouldn't (couldn't) refuse to do business with an ISP simply because they used Huawei kit. I'd imagine if you're working from home for the MoD different policies apply, and I would expect similar at enterprises that are corporate espionage targets.
On a practical level I'd encourage anyone technically minded enough to consider separating their home network with VLANs and implementing firewall rules to prevent inter-VLAN routing by default. IoT devices all want to hoover up as much data as possible, isolating them, including from each other is a good start.
If you have CCTV on the network, put that in its own VLAN and prevent it from phoning home. You can always VPN in to check it remotely.
And stay on top of software updates!