I've been in a similar situation. I did the following
- pay off all debt
- put max possible in ISAs. Some in cash, some in low-cost tracker funds if you are investing for more than 5 yrs.
- made a long term plan with financial adviser.
IFAs used to work on commission, meaning they would sell you the thing with most commission, not the one that was best for you. now they are not allowed to take commission, but the up-front costs to you are much higher. So make sure you have an IFA who really works for you. Mine did a good review of everything going on in my life (current investments, house, pension, school fees etc) and then made an overall plan.
If you do want to go it alone (I did for a few years, until the sums I was investing got too big), then that can work fine. I recommend basic, low cost tracker funds rather than anything clever. A tracker that follows the FTSE-100 with a 0.25% annual charge is a far better bet than a fancy investment trust with a 2% annual charge. The fund has to do 8 times better to beat the basic tracker, and that is almost impossible.
You can buy tracker funds and ETFs though various online platforms like Selftrade and www.hl.co.uk/shares/share-dealing, and it is pretty cheap & easy now.
One key thing to watch is the annual charges. 1% or 2% sounds low, but if your fund is making 7% per year and then 2% of that goes in annual charges, then you are making a LOT less. IFAs and many funds hide away info about things like annual charges because that is how they make money.
And finally, all my advice is based just on my own luck and reading of stuff online - it has worked so far, but do take all financial advice with a large pinch of salt.