Those aren't vandals they are thieves, >:( vandals wouldn't know what to do with a potato :( it is soul destroying to say the least but at the end of the day the spuds have done the land some good and the thieves have dug it over for you :D
Hope your friend phoned the police and got it logged with a crime number, don't let it spoil the memories of your holiday or deter you from your lottie, think of it as just a couple of quids worth of seed pots and start preparing for next year, in fact plant some more for Christmas. ;)