Well, without knowing the marks for this question it's hard to say how to structure it, but how does immigration affect consumers, firms, and the government?
- more demand due to population increase: good for firms and for overall expenditure, but may lead to inflation (AD increases due to consumption increase: arguably could be somewhat offset by increased imports, if immigrants want ingredients etc from their original country which can't be found in UK)
- larger workforce: good for firms (more competition, so larger supply of human capital, which can lead to wages being stagnant - this reduces their costs of production and could lead to either lower prices for consumers or larger profits for firms which they could invest in r&d. or just, like. take home in the form of increased bonuses), less good for consumers/rest of the population: more competition for jobs = lower wages, especially in unskilled work. can also lead to higher unemployment levels, if there aren't enough jobs to go around.
This isn't much, but fully evaluated it should give you hopefully around 5-600 words at least! I hope this was somewhat helpful :-)