The 200k Question?

I would say that assuming you build a well diversified portfolio, the two risks you have of losing a serious chunk are a) platform fraud and b) a serious economic downturn with related property crash. The other big risk is liquidity risk, i.e. You invest but can't get the cash out in 18 months when you need it.

I think the risks for a) are very low (especially for FCA regulated platforms) and b) are low but anything could happen with brexit (although presumably the property you are buying would also fall in price). You need to make your own assessment of both risks and decide if you are comfortable investing.

If it were me, the first thing I would do is put the cash in "access" style accounts so I get an instant return and maintain liquidity and then start dripping amounts into higher risk platforms as I find my feet.

So I would start off something like:-

Assetz Capital QAA account 60k (earning 3.75%)
Assetz Capital 30DAA account 60k (earning 4.25%)
Market Invoice 80k (earning 5-7%)

This will give you around 10k pa income off the bat and all will be accessible within 30 days or so. Your liquidity risk is extremely low in this structure.

I would then start investing in individual loans in Assetz, funding secure and maybe ablrate, lendy and money thing....but I would probably limit this to £50k or so (depending on how confident I got) and I would make sure I was fairly well diversified (no more than 2-3k per loan) and the loans I were choosing would be ones I could sell very easily. This will boost your returns.

This is what I would do but it depends on your attitude to risk.

£85k in a 12 month FCA protected account with Ford Money @ 1.7% is a risk free option. 

Consider Assetz instant/30day accounts & Octopus Choice for around 4%

I have some funds in a corporate bond tracker @ 2.5% and various higher risk bond funds @ around 6%

I am not sure stock market investment is advisable in your case due to the limited timescale.

Before considering the keep it all in the Bank suggestion, think about if your own property plans would still be viable if market conditions were so bad that solid platforms could not meet their instant access obligations.

Is there?

I've looked at Collateral a few times but there are not many loans.  There's only been 2 on the PM for the past few days and another few on the SM (woth a few days remaining).  I wouldn't risk diversifying between so few loans for such a short length of time (and in such high risk loans).

Also, loans with short day (eg 11 days) still sells

Getting money out of specific loans on a certain day is serious risk. 

Already we see:

- seasonal buy and sell times,  eg can be difficult sell without discounts in March as many sell re tax year end
- platforms can become unpopular very quickly and unless you are prepared to offer heavy discounts and be lucky you may not be able to sell until loan term
- generally a particular loan can be popular to start with but some poor info later and again you will be in for term
- loans that go into default can take 6-18 months to get some of your money back if you do.
- getting £200k invested across platforms and loans will take some time

Bottom line needing money back at a certain time is high risk and as soon as you start putting money in you will need to start taking it out again.

Saying that, today is quite a good time to sell and I think I could probably get back 80% of my portfolio within a week another 15% within a month and the rest eg possible defaults/problems over a year all without discounts. Tomorrow these numbers could significantly change.

If you put your amount of potential risk in a number of platforms eg £40k per platform and if 2 platforms have problems when you need the money you could be £80k short?

My thoughts, you are prepared to loose £30k, put that in and earn some decent returns on this over the next 18 months and hope it us a good time to sell in 12/18 months.

In this scenario I would recommend to go for auto-investment maintenance free accounts with quick and easy exit:
1.  Assetz Capital 30DAA - 4.25%, 30 days notice to withdraw.
2.  Bond Mason - 6.5%,  sell out is usually within few days.
3.  Growth Street - 5.9% (constantly declining, but hopefully won't go below 4% by this time next year), the loans are 1 month term, so no more than a month to get your money back.
4.  Funding Circle - 7.5%, selling out is quick as SM is very liquid.