can anyone help me in this please

Hello to all

My cousin was charged of Sexual Assault in Canada and he has left Canada without facing trial and Fingerprints as there was a threat to his life , his Gf lives in UK and she is Citizen of UK , Will it a Problem for him to get Fiance Visa in UK ? Will it be a problem for him to Enter UK with his Tourist Visa also ?
Does British Border Security got a access to Canadian Criminal Record ??

Looking for replies from Experienced people on this Website.

Thank you in Advance