Pro-Imran graffiti appears outside Sharifs' office in London.

LONDON -- A pro-Imran slogan was spray painted on the wall of Stanhope House, the building where former prime minister Nawaz Sharif's son Hussain has an office, on Monday, in an act that constitutes 'criminal vandalism' under UK law.

On Monday evening, a 'die-hard' supporter of PTI Chairman Imran Khan, British Pakistani Shayan Ali posted a photo on social media where he could be seen stood against the boundary wall, which was spray painted with the words: 'You can't kill IK chor'.

The phrase is being construed by many on social media as being targeted to the Sharifs, whom Mr Ali has for months been heckling and confronting outside their home, office and public places.

The slogan appeared just days after Mr Khan was shot and injured by a gun wielding critic at his rally in Wazirabad.

Mr Ali was briefly detained by Met Police officers last month when a PTI protest outside Avenfield House, where Nawaz Sharif resides, went out of control. Mr Ali is routinely seen outside Avenfield House and Stanhope House, shouting anti-Nawaz slogans.

In one recent video circulating on social media, residents of Dunraven Street who live nearby Avenfield House are seen pleading with Mr Ali and his peers, begging...