Thanks Tabetha.

On getting the car back from the garage they told me it was a cylinder misfire that was causing the problem. However when I checked the spark plugs and found the dodgy lead after I had wiggled it back on, she did seem to run a bit better for a short time so I am going to try changing the set of leads to see if it helps. I do have someone who said they will look under the cylinder head for me if needs be so that will probably help with costs but I am still concerned that it could be a costly fix if there is something wrong with the pistons/valves etc