S-R lilac

Can any green fingered Blipper identify this plant please? 

The label reads 'S-R' on one side, 'Lilac' on the reverse.
Something must have been said about it to make me think I would like it but I have no recollection of what it was or what the plant is.

It was one of four unexpected purchases on Saturday, when I came across a plant sale in someone's front porch. Of course, I was interested to have a quick look and was taken out to the back garden where lines of pots were on display. 

The sale is part of a fund-raising challenge, with those taking part working to raise £100 in 100 days for the MS Trust. Someone had the bright idea to take advantage of the (friendly) rivalry between Orkney and Shetland, and make it a competition to see which island can raise the most. 
Of course, I had to do my bit to help Orkney.