Thank you so much for your reply.
I came along the A2 into Strood, over the bridge into Chatham, which I think looking at a map now is the old A2. I carried on along the A2 and the satnav told me to take a left into Medway Street. I turned left, but again, looking at a map, I didn't take the lane marked 'All Routes' because I didn't see that it said 'All Routes' at the time and also it looked to me like a bus lane!
I couldn't turn around either because it looked to me as if I'd gone too far and it had become one-way. It really was a case of damned if you do and damned if you don't by then.
I think there should have been a sign at the junction between the A2 and Medway Street. Something to draw your attention to it being a bus garage and only for buses, something to make you carry on on the A2 and go around because Medway Street is a large bend and you can't see anything until you get round the bend and by the then, it's too late.
Like I said in my first post, there was a lorry directly in front of me so he must have been using a satnav too. The bus drivers didn't take any notice of me, they must be used to it I guess.