Personally i wouldnt worry about a solicitor at that point. Big waste of money. You will get a legal advisor at best and all they will do is make sure that the po po dont beat a confession out of you or use appresive methods, which is highly unlikely.
We dont live in an american law show where a solicitor comes in and ties the police up in knots and mugs everybody off and you get off scot free. Big money is not in minor criminal law cases, most decent solicitors will go into other areas of law, property etc.
Honesty is the best policy, only answer questions your asked. They will ask you to tell them in your own words what happened so make it brief and truthful.
Id be surprised if they wasted there time with it if im honest though.
And you obviously didnt want to waste police time by calling them out to a dead lampost, they have better things to be doing, you cant exactly exchange details with it. Worst thing youve done is not report the accident at the police station. As said no one was hurt, its a lamp post.