The UK's communications regulator has published useful guidance in relation to Powers of Attorney and Deputyship Orders.
The guidance highlights the importance of both Telecom providers and consumers understanding the powers created by these legal documents and how they should be used in practice.
Ofcom requires all telecoms providers in the UK to offer third party bill management. This allows a customer to nominate a friend or relative to help manage their account. The third party can receive copies of bills and can pay the bills, but does not become liable for them. The customer should contact their telecoms provider to set this up.