The preferred way of securing designated pipeline land is usually to use existing road, rail or powerline easements.
However, if the pipeline needs to cross private land, you will have to consult with the landowner about obtaining land for your pipeline.
These discussions will usually result in the creation of an easement on private land in return for some form of compensation. If the landowner refuses to negotiate with you, or refuses you easement access, you can apply for a Part 5 permission.