Western double standards

Sri Lankan president had to cancel his UK trip since he may face arrest in UK as under the principle of universal jurisdiction, war crimes and crimes against humanity can be prosecuted in UK even if they were not committed in the country. The foreign minister of Sri Lanka has been advised by their British counter part that the current Sri Lankan government must demonstrate its unconditional commitment to democracy. I do not understand what right they have to judge other countries for their commitment to democracy. I wonder if the British will offer a similar treatment to a visiting current or former US president for war crimes committed in places like Iraq or Afghanistan.