Paul, in some respect it doen't really matter (if you're investing for the long term). Mean cost averaging will even some of the sting out of the correction. However, if you have a conviction that there will be a correction (that's greater than say 7 - 8%) why would you invest now?
If your research suggests such a correction and you have the conviction you'd probably be better off shorting the market through one of the many ETFs out there.
Alternatively keep the cash in the bank and try to guess when the correction is over before investing.
By personal view is that for the long term 10+ years the correction is just another buying opportunity (but one that is not stopping investment in the present). My experience of most funds and ITs for that matter is that a correction affects all classes. The exception (in theory) is the absolute funds, or something like the Ruffer Co offering which is much mentioned on this forum, whilst of course some sectors will be effected more than others. I'd therefore suggest avoiding financials and mining focussed areas (such as overweighted in the FTSE 100) and look beyond these shores.