An MSP has accused the Government of trying to cover up a glitch in the 999 service in July that severely disrupted calls to the Scottish Ambulance Service. The incident occurred on July 21, when a technical fault hit all three Scottish dispatch centres meaning that they could only receive a limited number of calls. Inverness staff were the first to encounter difficulties at around 1am. The problem hit Edinburgh at 9.42am and then the Glasgow centre a few minutes later. Calls to the centres were diverted to England and Northern Ireland, and all the centres were fully operational again by 3.30pm. Labour’s Jackie Baillie says that she only found out about the problem by chance during a recent visit to the Northern Ireland Ambulance Service in Belfast, where some of the emergency calls were diverted. Ms Baillie has submitted a number of questions to the Scottish Parliament relating to the incident. She said: "The reason that we have three centres is to build resilience into the system and this kind of major failure should not happen. "It is reassuring to know that 999 calls continued to be handled from Northern Ireland and England, but we need to know what impact this had on response times. "Perhaps the most shocking aspect of this situation is that we only found out about it by accident because I was on a visit to Belfast. "Patients could have been put at risk if ambulances took longer to reach them, yet the Scottish Government appears to have tried to keep it secret." The ambulance service said it was working with BT to ensure there would be no repeat of the fault. A spokesman said: "The Scottish Ambulance Service's contingency plans for this scenario are for calls to be routed to Northern Ireland Ambulance Service and North West Ambulance Service control rooms, who relay information to Inverness, Cardonald and Edinburgh Emergency Medical Dispatch Centres (EMDCs) via an alternative phone system. "These contingency arrangements were successfully implemented and both Northern Ireland Ambulance Service and North West Ambulance Service passed call information to our EMDCs, who continued to dispatch ambulances to patients in need throughout the course of the BT failure. "It is reassuring that contingency plans developed for such scenarios worked with the minimum disruption for patients. "We have reviewed the incident with BT and they have agreed to an action plan to ensure that there is not a repeat of this type of fault." Health Secretary Nicola Sturgeon said: "When a problem arose with phone lines last month, the Scottish Ambulance Service put in place their contingency plans to ensure the 999 service continued to work as normal. "While these contingency plans, which involved rerouting calls, worked well, we understand that BT are carrying out a thorough investigation to prevent any recurrence of this problem."