Any LL who doesn't do a credit check on a prospective tenant is a fool and asking for trouble. Mind you, there are some of those around. To be honest, there's probably as many slipshod agents around as LLs - some agent's are purely interested in their commission and dont have a vested interest in making sure that the tenant is reliable.
If your credit history is poor you can offer to pay, for example, 3 or 6 months rent up front - if you can afford it. Alternatively, you if you can find someone (usually a relative) to stand as a guarantor for you then this is usually acceptable. However, the guarantor will have to pass the credit check too, otherwise it would be pointless. The guarantor will be liable for the rent and any other costs if you default.