‘Diabetes damages the walls of all blood vessels both large and small and so does high blood pressure,’ explains Dr Gerry Rayman, head of services at the Diabetes and Endocrine Centre at Ipswich Hospital NHS Trust. ‘The combination can be highly dangerous.’

It is the damage that diabetes does to the large blood vessels in the brain that causes strokes. These blood vessels either burst and bleed into the brain, causing a haemorrhagic stroke, or become narrowed or ‘furred up’, allowing a clot to form and triggering what is called a thrombotic stroke.

This narrowing is made worse by high blood fat levels and high blood pressure - both of which are more common in diabetics - leading to ‘a triple whammy’ effect, as Dr Rayman describes it.

This is why controlling blood pressure is so vital. Indeed, the upper target for diabetics is a blood pressure reading of no higher than 130/80, which is lower than the 140/90 target for the general population.

A new survey published by the charity Diabetes UK has found over half of the 2.9 million diagnosed diabetics in Britain have erratic blood pressure. This is significantly more than the 30 per cent of the general population who have high blood pressure.

Diabetics die up to ten years earlier than non diabetics - this is mainly due to complications including stroke, heart attack and kidney failure.

But Dr Rayman says many people with diabetes simply don’t realise the risks.

Type 1 diabetes is an auto-immune condition that usually develops in childhood while type 2 is linked to obesity. High blood pressure is a risk in both, although the incidence is greater in type 2.

‘The problem is that some doctors will try to soften the blow of a type 2 diagnosis by saying it’s “mild” and not as serious as type 1 which requires insulin injections. Being told that it is “a touch of diabetes” and can be controlled by tablets instantly downgrades perception of the risks.

‘But every case of diabetes should be regarded as serious.’

High blood pressure is the second most important symptom to control in diabetes apart from blood sugar, adds Baroness Young, chief executive for Diabetes UK. She believes high blood pressure is becoming the norm amongst diabetics.

‘Diabetics need a structured education programme so they realise how serious it is and what the risks are and be offered support to manage their condition.’

There is now greater emphasis on controlling blood pressure in diabetics, using drugs such as beta-blockers and angiotensin-converting enzyme (ACE) inhibitors. But many patients fail to take their medication.

Blood pressure drugs often have side-effects including a dry cough, dizziness and stomach upsets -  and consequently research has shown that up to 50 per cent of patients stop taking their drugs within a year.

‘Drug treatment can be tricky in that some people suffer side-effects, but this can be overcome by trying different combinations of drugs,’ says Dr Rayman. ‘The worst thing patients can do is give up taking the tablets completely.’