Depends on the accent and the person - some are easier than others and there is a variation. Including myself from Liverpool. People when they think 'Scouse', they think scally. But most people who arent scallies speak clearly enough including myself. I never had people misunderstand me but some people (usually very posh or strongly accents people themselves) have remarked on it (sometimes positively would you believe).Though non English speakers have struggled when i speak with family. But direct conversations - no issues. People in the US just assumed i was Irish.

Same for Glaswegian too. There is an accent spectrum, which i noticed when i lived there. If you only spoke with other Weegies then it would be stronger. Depends on person and if they mumble, speak fast and use lots of dialect. Also, age. I understand all 3 but if you came from the South or overseas and only heard telly, you would struggle. i know Geordie the least but i do like it the most. I would love a NE english accent but alas.