Poster printing often can't be done at the last minute because it's a lengthy process and there are limited places to do it. Earth Sciences offer in house printing up to AO but must be contacted in advance to check availability. The service is offered to non ES students for 20 quid, although preference is reserved for ES students. The University print services also print AO. Details of the UoB print services are here. It is best to call in advance to check how long printing will take. Services offered but The Students Union Print Shop can be found here. If these options fail there are some local businesses which offer printing, although they tend to be expensive.
The university have training and learning resources including how to use powerpoint to produce academic posters. These are available from the link below.
UoB Resources
For those of you who like Latex this is a good resource.
Latex Template
Adobe Illustrator is another great tool and this tutorial shows you the ropes.
Adobe Tutorial
Or you can download a guide to Adobe Illustrator.
Adobe Guide
You can find plenty of templates to base your poster on with a little help from Google!