Hmm.
OP, Many people here will be reading your account situation with a mixture of wonderment and envy- you've both done very well for yourselves. There are few people of your age with such a large amount of savings, no mortgage and a family. Congratulations, if there were more like you the country would not be in nearly as bad a state as it is now.
That said, I'd suggest that your number 1 priority is to keep your situation on a similar track. Firstly I'd suggest that you establish exactly what you would like to achieve in the medium-long term. Does a tertiary education for your child/children seem like a possibility? Will your husband like to retire early? Once you have an idea of that, then you can start to work out whether your current (excellent) course of saving £9,000 a year will let you achieve your desires. If not, then time to look elsewhere.
A note of caution regarding buy to let. You need to be very sure of the sums, as it can turn sour rapidly, especially in the current market. People generally think of the monthly rent cheque whilst conveniently forgetting management fees, empty periods, repair and maintenance, groundrent, letting agent fees, strife with tenants etc etc. The net income may be comparable to a savings account, all told. But the extra risks are massive. I'd say that, converse to accepted wisdom in the UK over the last 10 years or so, buy to let is one of the riskiest things one can embark on. Partly due to the risk of leveraged losses if a mortgage is involved (ie a 70% LTV mortgage on a place that falls in price by 30% means 100% of your deposit is lost) but also because it is a very illiquid asset (ie it's difficult to sell quickly).
See some sold prices near me- carnage.
www.houseprices.co.uk/e.php?q=138%2C+sn2+1fe&n=100
www.houseprices.co.uk/e.php?q=16%2C+sn2+1fd&n=100
I'd say that if you are not happy with the prospect of a 30% drop in the value of a property you would buy, then leave it alone. It is not a 'safe' investment, despite all the media spin and the British obsession with it. Many have and will lose their shirts over property. The market is not in a good position, just because prices have dropped a bit does not make them 'bargains'. Property is still massively overpriced compared to long-term averages, and seems likely to revisit those levels in due course.
There is no reason to balance what you feel is an 'over cautious' approach with a reckless one. In my opinion, your current path has been common sense, and not over cautious, and others have been reckless. The 'norm' has been skewed towards too much easy debt and little consideration of repayment. It may appear that others are doing better, but the reality is likely to be very different. If anything demonstrates this properly, it is that you have no debt and lots of assets, and most other people(especially your age) have loads of debt and little 'net' assets, even if they do have a smart car/big house etc. Debt is public enemy number one for people's quality of life as it robs resources to pay interest.
If you would like to start a business in future, the best thing to do is keep saving as cashflow is the killer to start with. As for investing, the work adviser sounds like a decent place to start(I assume he is an 'internal' guy rather than a salesman who visits the office) but do be wary of commission-based salesmen, as they can often recommend unsuitable products in order to maximise their paypacket. A fee-based IFA would be a place to start. Maybe some managed funds would be worth looking at in order to gain some equity exposure, but it is definitely something you'll have to take an active interest in if the best results are to be obtained. Be suspicious of funds with whopping management fees. The adviser will explain all this better than I.
Overall though, A*, keep up the good work and don't worry, you're in a great position so keep it that way.