What percentage of my UK salary should I invest monthly?

Hi guys,

I'm finally in a position where I can start investing regularly after building up my emergency fund. I've opened a Stocks & Shares ISA with Vanguard but haven't pulled the trigger yet on any investments. Some websites say to invest 10-15% of salary, others suggest "as much as you can afford."

Would love to hear what percentage of your salary you invest, and whether you include your pension contributions in that calculation?