Stocks & Shares ISA v Cash ISA v Savings

SomersetSaver

Hi please can I get some advice to help me with the age old question about how to decide how to split excess income between S&S ISA, Cash ISA and savings accounts.

I seem to have gone about my finances back to front in the past, and have always tried to channel surplus cash into an S&S ISA up to my full allowance this year, with some savings offset against my mortgage. I see the S&S ISA as being for retirement and have never had Cash ISAs at all (mainly because my cash was offset against the mortgage).

I now don't have an offset mortgage and so have been building up my savings, via regular savers and various instant access accounts, moving round chasing the best rates as far as I can. I also invest monthly into an S&S ISA, which I'd intended to fill to the full limit.

I've also now got to the point where I have 3 x my gross income as a buffer in case the worst happens, and am saving up a certain amount each month to replace my car in 2 or so years time; both these pots of cash I see as me not needing access to unless the worst happens.

I am then saving other money towards other 'stuff' - holidays, day to day items, home improvements, perhaps paying a lump sum off the mortgage each year etc. - which I would see as perhaps needing to keep more as instant access.

However, I can't get my head around whether I'd be best putting some of this 'locked away' cash into a Cash ISA and thus split the ISA allowance between S&S and Cash, or to continue putting the full amount into S&S ISA and basically pay interest on my savings accounts.

I don't want to lock the money away into my pension as I'm already saving into that and have a probably irrational fear about the money being locked up and me needing access to it one day and being unable to - hence going for ISAs.

I'm currently saving about £1,000 per month into savings accounts and am a higher rate tax payer.

I know it depends upon attitude to risk and all that so I'm not expecting anyone to give me a full answer, but I seem to be struggling how to work out what the things I need to consider to come to a decision on what's best for my money.

So I'd be v grateful for any help anyone can give me, please!
Thanks in advance
SS