As said, you've got to tell your insurance, but after you are prosecuted (otherwise you are not necesserily guilty...), or you could face your policy being cancelled/declared void due to failure to disclose material fact, and if you've just knocked somebody down, or been stopped by the police and have to produce, that's not good!
You are not hugely over the ACPO guidelines, so I'd expect £60 and 3 points.
Usually you are better off accepting the fixed penalty, but if you are at risk of losing your license then I'd look in at
www.roadsidelawyer.co.uk - it's a good site to look through when you are bored, and can be really interesting (if you are boring?
)
Insurance premium wise, it depends on your age and such, but due to the high number of SP30s ("Exceeding statutory speed limit on a public road"), I wouldn't expect an increase (or not much anyway).