Graham Hughes is getting set to become to first person to visit all 201 countries without flying or using private transport.
The 33-year-old Liverpudlian began his expedition on 1 January, 2009, and had visited all countries in November last year.
However, the Guinness World Records said they could give him an official record-holder title because he had entered Russia illegally.
To finish his Odyssey Expedition, he is now travelling via train to Poland, after which he will cross the border legally into Russia on a bus.
His first visit to Russia involved him wading through the River Narva from Estonia without a valid Russian visa.
Hughes told the Telegraph: "The visa into Russia cost about 150 quid and I was on a shoestring budget, and travelling to as many countries as possible, very fast.
"[The Guinness World Record's decision] is completely understandable, because they don't want to encourage people to do illegal things."
He caught the train from London this morning, tweeting: "Made the bus from Victoria by the skin of my teeth. Got a 25 hour coach journey ahead of me, just like old times eh?!
"Au revior Blighty. See you again in a few days!"
Hughes is due to arrive in Russia on Tuesday night or Wednesday and will return to the UK on Thursday a record-holder.
During his trip, he lived on an average of £10 per day and completed the journey by sleeping on countless sofas. In the first two years of the trip, he spent about £7,000 but managed to get this down to £3,000 for the remainder.
Hughes managed to "tip-toe" into North Korea by visiting the 'Peace Village' set up in the middle of the Demilitarised Zone between North and South Korea. He went into one of the five huts that straddle the boarder and walked to the far side.
Speaking about the experience to the Independent before he left for Russia, Hughes said: "It is not the lonely experience that you might think. You're forced to make conversation with people.
"When you're on your own you talk to more people. Very often it is money that seems to stop people travelling. They think it will be really expensive. But it is cheaper to go and travel than to go to university. It's cheaper than having a flat in London."