Increase your longer runs up to half your weekly milage but do this only once a month.
Do some 5k parkrun races at least one a month.
Every two weeks do some speed track work and/or tempo runs/ tempo intervals.
Hill work can be incorporated into the parkruns if you can find a suitable course.
I did this kind of training and on less than 35 miles a week did last years GNR in 1:31. Didnt even feel the hills people speak of and flew the first 10k in 42 minutes.
Miles 8-11 were tough pace wise but because I had done long runs of 13+miles I knew I could run it so I excepted the flutulations in pace and come mile 11 just went for it and put the hammer down. Thats what parkruns give you and often what gets a pb for me.
So, more miles, threshold work, dedicated track work.
Also if you can safely lose any weight, and I emphasise safely, think of ways you can. It does make you faster if all else is equal. Right now I am just under 70kg my HM was done at 75kg and I know I am faster and stronger now.
Fortune favours the brave