Generally, if you are investing and you want access to your cash in the short term, you are better investing your money in a cautious/low-risk portfolios. In these types of portfolios, your investments are weighted more traditionally in safer investments such as: bonds and cash. Meaning that your money is weighted less in riskier investments that are more susceptible to market volatility.
Volatility is the amount your money fluctuates in value. As time goes on, day to day volatility becomes less and less important. So if you plan on investing for the 5+ years, a higher risk portfolio could be a viable option. But in the short term, it is better to go for a lower risk because if the market suddenly drops, you may have to wait a while for your investments to recover.
Other options could be to save your money rather than invest. A lot of high street banks offer fixed rate introductory offers on Cash savings or Cash ISA’s, so it might be worth checking them out as well! I found this article on The Money Saving Expert which you might find useful. There’s also a great article here on saving for a mortgage.
With anything like this, I have to caveat that this isn’t investment/savings advice. This is more general information you can use when making your own decision. With any sort of investment, your capital is at risk.
All the best,