This comes after he took to Twitter to voice his unhappiness over L&G's decision to stop taking phone calls. In his tweet, Mr Harper said L&G could expect "little support" from him.
He said: "If a client's policy required regular and ongoing response then we would move it away. It would be a hassle to do this, but would ultimately mean no extra advice costs for the client and a reduction in time spent dealing with their accounts."
Advice firm IFS Wealth and Pensions said it has encountered similar problems with L&G's services.
Ricky Chan, director and financial planner at IFS Wealth and Pensions, said L&G’s approach "prevented IFAs from doing their jobs". However, Mr Chan said he has not increased fees as a result of the issues.
He said: "I can understand why providers are [digitalising] as part of cost savings and efficiency. But it does create difficulty because sometimes you just have a simple question and you wish you could just pick up the phone to speak to someone, rather than waiting two days for a reply over a fairly trivial matter."
Nathan Long, senior pension analyst at Hargreaves Lansdown, said if digitalisation ends up creating a poor service, then this could serve to undermine the quality of advice given by advisers.
"If providers get rid of human interaction, they risk hollowing out the value of their propositions," he said.
"If an adviser's quality of advice is undermined, because it can't get information from providers, then this is a large issue for all involved."
In response to the issues raised, L&G said: "This relates to the Mature Savings Digital Response Team only within L&G and was introduced over 18 months ago with a dedicated team who work more flexible and longer hours to make sure we reflect the differing needs of financial advisers in a more digital and extended working day.
"The introduction of the email digital service followed surveys and the changing needs of advisers recognising numerous requests on different products were taking lengthy calls.
"Email enquiries are dealt with within a published 48 hours, often this is exceeded and can be far quicker than a telephone call which is then referred to an administration area. Since launch, improvements in automation as well as further advisor surveys allows the service to consistently evolve and meet or exceed published service standards."