Personally I'd veer towards paying off the mortgage but I generally don't like having debt unless I'm confident it is earning me more than it costs. Paying off the mortgage now eliminates the risk that your investments tank to the extent they are no longer worth more than the mortgage.
If you are good at investing money it probably makes more sense to have the capital 'out there earning more money'.
I'm in a similar position (although with not as much invested) and am thinking to take the majority of my ISA and pay off some of the mortgage.
Up to know I'd been paying the mortgage and bills with my brother, but he's moving out in April and the mortgage needs renewing. If I do nothing, it will go up about £300 a month. If I use some of my ISA, I can bring it to slightly lower than now. I currently put £800 into savings/investments a month, so I'm fairly sure I can afford the increase, I just wont be investing like I was, but then I see paying the mortgage as similar to an investment. I still have 17 years to go, but basically when I decide to move out of London, there are some places I could probably buy outright.
I was going to only sign a 2 year deal, in case I don't like know having the same disposable income and want to move to the (cheap) countryside. If I sign a 5 year, but sell up in 2 or 3, do I pay a penalty?
Given I'm told things are peaking in the next few months, is a tracker a better option than fixed?
The options I've been shown, a 2 year tracker has a lower rate (3.7ish) than a 2 or 5 year fixed (4.6ish) so the shorter tracker seems a no brainer?