I would think £400 would be a fair estimate.  I guess if you saved that much a month, that's already more than what most freshies would earn a month in Malaysia.  Also, the experience of working in a different culture can be beneficial too.  Yeah, living in UK maybe far from family and friends in Malaysia, but the Malaysian community in London is massive and always a house party/drinking/clubbing going on.

I am glad I have moved to Switzerland since January, more benefits and no major bills to pay once I get my salary.    Downside is I can't speak German "yet" and it can prove troublesome at times.

let say i am not UK grad but eligible for high skilled migration, should i contact agents instead?
any contacts that i can get?

it works this way, lets say your annual salary is £40k per year. out of £40k, abt £5.3k is not taxable called (income allowance). then the first 2.2k of your 40k will be taxed at 10%, your next 2.2k to £34k will be taxed at 22% and finally, you will be taxed 40% after 34k. so you might get more for the first few months, but lesser as month to come, or some company will spread it over the whole year.

so it is not that if you get 40k perannum, 40% will be gone, but part of them are taxed at 10%, 22% and 40%. on top, put in another abt 7% for national insurance.
it is not actually. as long as you have the qualification and qualities, you can get a job easily.
although the taxes are high, but it is not bad earning pound. because the cost of most items are cheaper if compare to malaysia.

example. if you earned rm30k a year in malaysia, you have to use a year salary which is rm30k to buy a kelisa. but in uk, if you earn £20k a year (after tax abt 16k, where £23k is the standard average salary of a fresh grad), a good new car of abt the size of kelisa (e.g. ford fiesta) is abt £8k only.