Women at high risk of breast cancer could be forced to endure long waits for genetic testing and extra screening for the disease because NHS services for such patients receive too little money, cancer experts have warned.

Some experts in Britain's most common cancer are expecting the NHS to face increasing demand from women anxious about developing breast cancer and keen to be tested after actor Angelina Jolie revealed on Tuesday that she had undergone a double mastectomy that had reduced her risk of getting breast cancer from 87% to 5%.

But fears have been raised that the NHS's 35 genetic testing centres, which test about 8,000 women for the BRCA genes – which can increase the risk of breast cancer by up to 80% – will not be able to cope with a planned expansion in the number of women eligible to go there.

The NHS is expected to at least double the number of women who are offered genetic testing as a result of forthcoming new guidance being finalised by the National Institute for Health and Care Excellence (Nice), as part of a drive to improve early detection and treatment of a disease with which 50,000 women a year are diagnosed.

Diana Eccles, a professor of cancer genetics at Southampton University who also works at the NHS's genetic testing centre in the city, welcomed the fact that Nice plans to lower the threshold for the risk that a woman is carrying the faulty BRCA1 or BRCA2 gene, based on how many of her relatives have had it and at what age, before she can be tested. It currently stands at a 20% probability but is due to be halved to 10%.

"Nice's guidance means that you won't need to have such a strong family history [of breast or ovarian cancer] to get genetically tested, so more people will be able to access it", said Eccles. "But lots of the 35 genetic centres don't have enough staff to offer it to everyone. We are pretty busy at the current level of activity. If the level of activity doubles or trebles as a result of the guidance, we might struggle to deliver a timely service. People may have to wait for an appointment. There will be funding needed."

Currently women deemed at high risk of breast cancer wait for up to 18 weeks to be tested. But Eccles voiced concern that the expected increase in number of patients could lead to some women having to wait for up to a year, as used to happen, unless the expansion was backed by extra money.

"Some years ago, before services were sufficient to cope, people would wait for maybe a year for an appointment. That has changed with investment. My concern is that long waits could start to happen again," she said.

Gordon Wishart, a professor of cancer surgery at Anglia Ruskin University and former senior NHS breast cancer surgeon, said he shared Eccles's concerns and added that Nice's plan for larger number of women at risk of breast cancer to also receive extra MRI screening could also be undermined by a lack of resources.

"Nice is no guarantee that what's in the [new] guidelines will be available in your local hospital in a few months' time, as it should be, because it's going to require funding. My concern is that unless there's additional funding to implement the guidance then it may not represent real progress and people may wait longer for the results of genetic testing or may not get access to the additional breast screening they require," said Wishart.

The NHS's care for women at risk of breast cancer has been "good in some areas and substandard in other areas", he said, citing the previous refusal of NHS primary care trusts in some areas to give women at moderate rather than high risk extra MRI scans, despite Nice recommending they should have them, because of a shortage of cash.

Pleas to the primary care trust in Cambridgeshire, where he works, "fell on deaf ears", Wishart said.

The new NHS guidelines, which are expected in the summer, had to be implemented in full across the whole of England in order to avoid a similar postcode lottery in access to MRI screening developing again, he said.

Jolie's decision to go public about her risk-reducing surgery "must give a lot of women hope that things are going to change and that if they have a strong family history of breast cancer they are going to have access to testing and a variety of options [to manage their risk]", Wishart added.

The charity Breast Cancer Campaign said a recent Nice survey of cancer geneticists at genetic testing centres in England, Wales and Northern Ireland had found that high-risk women's access to MRI scanning was uneven and depended on where they lived.

"One issue highlighted was that although 65% of cancer geneticists reported that women eligible for annual MRI scans received these, there was regional variation in accessing MRI. This regional variation was attributed to a lack of local resources," said Mia Rosenblatt, the charity's head of policy and campaigns.

But Breakthrough Breast Cancer, another charity, praised the NHS's care of such women. "The integrated process provided by NHS genetic services is fantastic, combining risk assessment, lab testing, genetic counselling and surgery," said a spokeswoman. "A personalised approach is taken with each patient, which is important when considering individual decisions."