If you and your husband can get the next day off work @KatieBr, I think he should go with you on the first day, after having booked an extra night at the same hotel - if possible - just so that you can spend some nice time together in an amazing city.
However, I strongly believe that you should make it very clear to your DH that you want him to come along for his excellent company, and not because you couldn't manage central London on your own! So please have a serious talk with your DH about putting you down insidiously like that, he might not even realise he is doing it, as far too many generations of men have grown up in a misogynistic household, and have learned to talk to woman like that.
Obviously, misogyny needs to be, in fact must be, stopped. Luckily, an otherwise kind and intelligent man (like your DH ?), should agree with this from the start, and be able to learn how to understand, agree with, and implement this behaviour. reasonably easily.
I hope you have a great time OP, in whatever way it plays out.
But I am quite puzzled about why any business would decide to have a training day in one of the most expensive places in the country?