Thanks everyone for the replies and the debate it provoked (I take the constructive criticism in the benevolent sense it's meant!).
I s'pose my OP might have, to the chagrin of Brendan, conveyed the misleading impression that AAM experts were advocating paying off ones mortgage above all else as an investment strategy. I accept that is not the case and I took on board the importance of prioritising reducing and ultimately eliminating the mortgage along with pension investment over other investment decisions. Hence I guess part of the reason I have ended up with an excessive cash pile as opposed to more diversified investments. I have maximised my AVC contributions for recent years progressively up from up from 10% (when I was paying full whack on the mortgage) through 50% of the maximum up to the present maximum. AFAIK I'm not permitted to add any more lump sums of backdated payments to our pension funds. That has led me into dipping my toes in stock investment in the last couple of years (from the time when I had the mortgage payment reduced to an inconsequential amount) and it's been a tentative learning experience, hence the reason its a gradual process of transfer of diversification.
Regarding the cash and the gold. I suppose that approach has grown out of my disaffection and disgust of banks over the last decade or more. I'm mindful of Ugolin in Manon of the Springs hoarding his gold sous in the pot under the earthen floor. I guess (without subscribing to the alt conspiracy theorists too much) the concept of having a portion of physical wealth in the form of gold if everything else collapses into mistrust (considering events in the last month in the US not a totally unlikely prospect I think) appeals to me somewhat. Incidently my gold and cash aren't hidden under the floor or in the mattress!
In addition to the AVC's we're lucky to also have the prospect of occupational pensions and the contributary state pension at 66 along with thanks to the UK pension thread, a full UK contributary OAP for me at 67, so I'm pretty happy about the level of provision I've made for the future .
Anyway, thanks to the insights offered here I shall continue to diversify further into stocks and equities over the coming year. Perhaps I'll report back in a year or so on how it's gone.