What is the best way to find out what type of mold/fungi this is?

I have found some mould or fungi behind my bath tub panel. It seems to be the results of splashed water. I’d like to know what it is exactly.

I’m in the UK. If I need more specific data about what species this is etc what type of lab should I send it to/can you name one in the UK.

I already consulted some labs but they said they only examine mold which use their air test or urine test etc. I’m thinking the easiest thing to do is just cut this out and send it to a lab but dont know which/where exactly.

Thanks.